Take the dough out of the fridge 2 hours prior to using. Do not uncover the bowl. Oil the bottom of a 12 by 16 sheet pan (or standard half sheet pan) with 3/8's cup of olive oil. You need to use a lot of oil!
Remove the dough from the bowl and place it into the pan. With your fingertips begin pressing the dough into the corners of the pan. You will not be able to do this in one attempt. Place plastic over the pan and let the dough warm up.
After 45 minutes remove the plastic and try to stretch it again to the size of the pan. Cover with plastic wrap and repeat process one more time until the dough has completely filled the pan. Cover the dough one more time and set aside. Preheat oven to 450f and set one rack to the lowest level of the oven and one to the highest.
Hand crush the plum tomatoes and drain the juice. Save the juice for another use. Add a ½ teaspoon of kosher salt to the tomatoes and set aside.
Mince the garlic and add to a bowl with a ¼ cup of olive oil.
Remove the plastic from the pan and if required press the dough into the edges. Right away layer the mozzarella cheese in an overlapping shingle pattern, leaving the outside 1/4 to 1/2 inch uncovered. Start with a corner. By pressing the dough down slightly you can lock the dough into the corner. Make sure the dough is layered completely with the mozzarella slices.
Next, add the drained plum tomatoes to the pizza. You can use 45 degree lines or spoon the sauce all over. Leave some open areas. Don’t coat it all. Take the garlic oil and drizzle 3 tablespoons of the oil and garlic pieces all over the pizza.
Place the pizza onto the lowest rack and cook for 12 minutes rotating the pan 180 degrees after 6 minutes.
After 12 minutes remove the pizza from oven and check the bottom for browning. If the pizza is well-browned, bake on top rack for 6 more minutes. Otherwise, leave the pizza on the bottom rack for 6 more minutes.
After 18 minutes of baking remove the pizza and sprinkle with the oregano and Pecorino Romano cheese. Bake for 2 minutes more on top oven rack.
If the Grandma pizza is not crisp enough on top, you can broil for 30-60 seconds. Watch very carefully though!
The total cooking time will be approximately 20-22 minutes. Let the pizza sit for 5 minutes before cutting and serving. Enjoy!