Italian Zucchini Casserole is the perfect way to use up all your summer zucchini! This delicious side dish combines thinly sliced zucchini, tomatoes, and onions that are layered with cheese, and herbs, topped with a garlicky breadcrumb mixture, and baked until bubbly.

Italian zucchini casserole with toasted breadcrumbs and basil garnish.


Zucchini is one of my favorite ingredients because it’s incredibly versatile and easy to grow.

I use it all the time, especially, in summer, and make this Italian zucchini casserole often.

It’s one I grew up eating, and one I hope my kids will make for my grandkids in the future.

The layers of tomato, zucchini, and onion with herbs, cheese, and breadcrumbs are just delicious and the perfect side to grilled chicken thighs or grilled pork chops.

While this zucchini onion tomato casserole is predominantly a summer dish, I make it all year and often for Thanksgiving!

Recipe Ingredients

All ingredients for this recipe are shown in the pic below and special notes are made in this bulleted list to assist you.

Ingredients shown: zucchini, Sicilian oregano, olive oil, tomatoes, Pecorino Romano, breadcrumbs, and onions.
  • Zucchini. I prefer to use medium zucchini for Italian zucchini casserole. Save the small zucchini for dishes like spaghetti alla Nerano.
  • Tomatoes. Beefsteaks or heirlooms are great as are plum tomatoes. Truthfully, any type of tomato will work since the dish is roasted uncovered allowing the water from the tomatoes to evaporate.
  • Oregano. I use dried Sicilian oregano (as pictured above) for zucchini casserole because it adds tremendous flavor. I recommend using the packaged dried flowers over the jarred version for best results.

See the recipe card for full information on ingredients and quantities.

How to make it

Each number corresponds to the numbered written steps below.

  1. Preheat the oven to 375f and set the rack to the middle level. Finely grate 1/2 cup of Pecorino Romano cheese dividing 1/4 for the breadcrumbs and 1/4 for the zucchini. Mince 2 cloves of garlic. Using a mandoline (with a safety attachment) or a sharp knife, slice 3 medium zucchini into thin slices, lengthwise. Thinly slice 2 large tomatoes and 2 large onions and set aside. Drain the sliced tomatoes and pat them and the zucchini slices dry with paper towels too remove excess liquid.
Italian zucchini casserole recipe collage group one showing mandoline with sliced zucchini and mixing breadcrumbs in a bowl.
  1. In a bowl, mix together the garlic, 1/2 cup of breadcrumbs, 1/4 cup of the grated Pecorino Romano, 1/2 teaspoon of crushed red pepper flakes, 1 teaspoon of Sicilian oregano, and 3 tablespoons of extra virgin olive oil and set aside.
  2. Oil a 9×13 baking dish (below I used two smaller baking dishes) and place a few layers of zucchini, then drizzle with extra virgin olive oil and season with salt and pepper to taste. Add a pinch of Sicilian oregano and some of the Pecorino Romano cheese.
Recipe collage two showing layering and seasoning of vegetables in two baking dishes.
  1. Add a few layers of onion and season with the salt, pepper, Sicilian oregano, and Pecorino Romano in the same manner.
  2. Layer the tomatoes and drizzle with some extra virgin olive oil, and season in the same manner with the salt, pepper, Sicilian oregano, and cheese, then sprinkle the breadcrumbs on top and add a bit more grated cheese. Drizzle some more extra virgin olive oil until the breadcrumbs are well-moistened.
Recipe collage three showing drizzling olive oil onto breadcrumb topping and finished dish after baking.
  1. Bake for 45 minutes or until bubbly. Much of the liquid should have evaporated at this point. If the breadcrumbs aren’t golden enough, you can broil them for 1-2 minutes but watch carefully to prevent burning. Allow the zucchini casserole to settle for at least 10-15 minutes before serving with your favorite main course. Enjoy!

Top tips

  • Slicing. Whenever using a mandoline it’s important to follow the manufacturer’s instructions for safety. Always use the safety guard and take your time when using one. You can 100% use a knife for this recipe.
  • Wetness. Drain the sliced tomatoes and pat them and the zucchini slices with paper towels to remove excess water. If the casserole is too wet after 45 minutes of baking you can carefully drain some of the liquid or pull it out with a bulb blaster or paper towels and bake for another 5-10 minutes before serving.
  • Seasoning. This is one of those recipes where the seasoning doesn’t need to be so precise. Depending on how many levels of layers you have you may need to use more or less. Keep in mind that Pecorino Romano is on the saltier side so you many not need as much salt as you’d think.
  • Let it settle. This Italian zucchini tomato casserole should be allowed to settle for at least 10-15 minutes before serving, but it can sit for longer and is also delicious at room temperature.

Spoon holding scoop of Italian zucchini casserole over baking dish.

More zucchini recipes

If you’ve been blessed with an abundance of zucchini, here are a few of my favorite recipes to try.

If you’ve enjoyed this Italian Zucchini Casserole Recipe or any recipe on this site, give it a 5-star rating and tell us about it in the comments below.

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Italian Zucchini Casserole

4.86 from 7 votes
Prep: 20 minutes
Cook: 1 hour
Total: 1 hour 20 minutes
Servings: 6
This simple but delicious Italian Zucchini Casserole combines layers of thinly sliced zucchini, tomatoes, and onions, topped with seasoned breadcrumbs and baked until bubbly.

Ingredients 

  • 2 large tomatoes thinly sliced
  • 3 medium zucchini thinly sliced lengthwise
  • 2 large onions thinly sliced – yellow, white, or red are all fine
  • salt and pepper to taste
  • 2 teaspoons Sicilian oregano
  • 1/4 cup finely grated Pecorino Romano
  • 1/2 cup extra virgin olive oil divided

Seasoned breadcrumb mixture (mix together)

  • 1/2 cup plain breadcrumbs
  • 1 teaspoon Sicilian oregano
  • 1/4 cup finely grated Pecorino Romano
  • 1/2 teaspoon crushed red pepper flakes
  • 3 tablespoons extra virgin olive oil
  • 2 cloves garlic minced

Instructions 

  • Preheat the oven to 375f and set the rack to the middle level. In a bowl, mix together the ingredients for the seasoned breadcrumbs and set aside.
  • Use a mandoline or sharp knife to make thin slices of the zucchini (lengthwise), tomatoes, and onions. Drain the sliced tomatoes and pat dry both the tomatoes and zucchini with paper towels before the layering.
  • Oil a 9×13 baking dish. Place a few layers of zucchini then drizzle extra virgin olive oil and season with salt, pepper, oregano, and Pecorino Romano cheese. Next, add a few layers of onions and drizzle the olive oil and season in the same manner. Finally layer the tomatoes, drizzle the oil and season. Sprinkle the breadcrumbs on top and grate a bit more cheese. Drizzle more oil if required. The breadcrumbs should be well moistened.
  • Bake for 45 minutes or until bubbly. Most of the liquid should be evaporated at this point. If the breadcrumbs aren't golden brown you can broil for the last 1-2 minutes but watch very carefully. Wait at least 10-15 minutes before serving so that the juices settle. Enjoy!

Notes

  • A large shallow baking dish with only 3 layers works better and cooks quicker than a deep dish with many layers of ingredients, but both will work.
  • Distribute a portion of the seasoning on each level.  Depending on how many levels are made, a bit more or less seasoning might be required.
  • Cooking times are a rough estimate.  Bake until most of the liquid evaporates and the zucchini is clear and tender.  If the casserole is wet after 45 minutes of baking you can carefully drain some of the liquid or pull it out with a bulb blaster or paper towels and bake for another 5-10 minutes before serving.
  • For more browning, the dish can be broiled for the last 1-2 minutes, but watch carefully.
  • Leftovers can be saved for up to 3 days and can be reheated in the oven or microwave.

Nutrition

Calories: 183kcal | Carbohydrates: 10.2g | Protein: 5.1g | Fat: 14.4g | Saturated Fat: 3.2g | Cholesterol: 7mg | Sodium: 164mg | Potassium: 169mg | Fiber: 1.3g | Sugar: 2.3g | Calcium: 116mg | Iron: 1mg

Nutrition information is automatically calculated, so should only be used as an approximation.

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4.86 from 7 votes

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22 Comments

  1. Bev Sherwin says:

    4 stars
    James @nd Tara, all your recipes are five star, I’m a huge fan, but this one I had a bit of a problem with. The taste was perfect, I loved it! But there was a lot of liquid in the casserole dish after it was fully cooked. I’m not sure if I did something wrong. The topping was turning dark, borderline burning, after 50 minutes, so I covered the casserole dish with foil, which probably increased the liquid. What could I have done better? Love you guys!

    1. James says:

      Hi Bev,

      I updated the recipe to include patting both the tomatoes and zucchini dry with paper towels. If the casserole is burning you can cover with foil at the end but yes it will trap the liquid. I do think patting dry will alleviate any issues. Also, at 375f, in my conventional oven, I had no color after 45 minutes and had to broil. All ovens are different, but I just want to confirm that you didn’t use convection. Thanks for liking the recipes!

  2. Nick Giglio says:

    5 stars
    We were given a few yellow and green nice large zucchinis over the past few days, and I made this twice. It was a really big hit! Very delicious! Your recipes are excellent, and we appreciate all the work that you put into them. I also made the deli style macaroni salad, and one pound disappeared in no time. It’s the first time I brined the pasta and added the mayo later. It was outstanding! I’ll be looking forward to all your recipes. Thanks again!

    1. Tara says:

      Hi Nick, we’re so happy you’ve made this twice and enjoyed it as well as the macaroni salad! Thanks for the great comment!

  3. C Cochran says:

    5 stars
    Delicious! Made this tonight. While baking, the house was filled with a wonderful aroma. While eating, our mouths were filled with fantastic flavors. Definitely worth the time to make.

    1. Tara says:

      We are so happy you enjoyed! The aroma is one of the best parts!

  4. Dawn says:

    Love ❤️ your recipes. They are very similar to my Nanny Guzzo’s. I’m making the Zucchini casserole today as I have a lot of zucchini. Keep up the great work.

    1. Tara says:

      We’re so happy you’re enjoying the recipes and hope you love this one too!

  5. Karen says:

    5 stars
    This recipe couldn’t have come at a better time. I had some zucchini, tomatoes & onions I needed to use up before going away for a few days. This was perfect. I’ll definitely be making this again.

    1. Tara says:

      We’re so happy you enjoyed it, Karen!

  6. Robin M McLean says:

    5 stars
    Delicious and easy to prepare.

    1. Tara says:

      So happy you enjoyed, Robin!

  7. MIckey Zalusky says:

    Wow, this looks amazing. Love that it can even be served at room temperature. I know the breadcrumbs help to absorb any water from the zucchini. Do you think salting and draining the zucchini before assembling/baking might help to eliminate the need for breadcrumbs (I’m diabetic and try to avoid bread for dietary purposes.) Definitely adding this to my recipe of Summer sides. Thanks for all you do Jim, Tara and all your taste testers!!!

    1. Tara says:

      Hi Mickey, while the breadcrumbs do absorb some of the water, they’re really there to add texture. You can omit them but Jim recommends replacing with some grated cheese for that textural element. Thanks for the comment and hope you enjoy!

  8. Gerrie says:

    5 stars
    Excellent.

    1. Tara says:

      We’re so happy you enjoyed this one, Gerrie!

  9. Judy Moreis says:

    5 stars
    Great Recipe!! Thanks

    1. Tara says:

      We’re so happy you enjoyed the recipe, Judy!

  10. Patty Young says:

    We LOVE your recipes. We even love the helpful hints you give us. It has made us become more interested in cooking again. I hope you continue!

    1. Tara says:

      We’re so happy you are enjoying the recipes, Patty! Thanks for the comment!

      1. Connie says:

        Tara, can this dish be made ahead of time?
        Maybe par baked then finished off at dinner time or sitting in fridge a day til cooked?

        1. Tara says:

          Hi Connie, yes, it definitely can be made ahead of time. Just warm in the oven, or even serve at room temperature. It’s great left over too with an over-easy egg on top!