In a Dutch oven, cook the beef, onions and pepper over medium heat until meat is no longer pink; drain. Add garlic; cook 1 minute longer. Stir in the water, tomato paste, mushrooms, pepperoni, sauce mix and Italian seasoning. Bring water to a boil. Reduce heat; simmer uncovered for 1 hour.
Meanwhile, for pasta, bring water to a boil in a large saucepan. Add the macaroni and pastas. Return to a boil, stirring occasionally. Cook, uncovered for 10–12 minutes or until tender; drain. Stir into tomato sauce. Transfer to a greased 13-by-9-inch baking dish (dish will be full).
Bake at 350 degrees for 30 minutes. Sprinkle with mozzarella cheese. Bake for 5–10 minutes longer or until cheese is melted.