Preheat oven to 375. Degrease a casserole dish.
Heat olive oil in a large skillet and add turkey sausage and break apart. Add oregano, Italian seasoning, pepper, onion and bell pepper to the sausage. Continue cooking until sausage is fully cooked. Drain liquid from skillet.
Evenly spread sausage mixture in the bottom of casserole dish and cover with tomatoes.
Sprinkle cheese evenly over tomatoes
Place pepperoni on cheese.
Bake 25-28 minutes. Cheese should be melted before removing from oven.