Heat oven to 350. Mix together the cooked noodles, ground beef, pizza sauce, pasta sauce and cheese soup. Stir in the diced pepperoni pieces so that the pepperoni flavor will be evenly distributed.
Place pasta mixture in a large 9×13 pan or two smaller 8×8 pans. Coat with mozzarella cheese. Top with remaining pepperoni slices.
If you are going to freeze the casserole now is the time to do it. Cover with plastic wrap and put in the freezer for a later date. Defrost and follow last step when ready to cook.
Place in oven and cook for 1 hour. Casserole dish is done when cheese has browned.