In a large skillet over medium heat, brown the ground beef with the onion and green pepper. Drain any excess liquid and reserve. Add spaghetti seasoning mix to the browned meat and blend. Add pepperoni and mushrooms and blend again.
Meanwhile, prepare the pastas as directed on the package and drain.
Combine the cooked pastas with the ground beef mixture in the baking pan. Add tomato sauce and water; stir to combine.
Add most of the cheeses and stir again, sprinkling the remaining cheeses over the top of the casserole.
Bake for about 30 minutes, uncovered. Serve warm in pasta bowls with a sprinkling of Parmesan cheese, if desired.