In a large mixing bowl, combine ground beef, cheeses, eggs, oil, cracker crumbs, green peppers, garlic, salt and pepper and 1 cup marinara sauce. When mixed, add mushrooms if desired. Put in loaf pan or glass baking pan and cover with remaining marinara sauce.
Bake uncovered in preheated oven for 60-75 minutes. Let sit 10 minutes before slicing, serve hot.
