Preheat oven to 350º Fahrenheit. While the oven is preheating, start to cook your pasta according to the package directions.
While the pasta is cooking, add ground beef and onion to a large Dutch Oven. Cook over medium heat until the beef is no longer pink and the onions are translucent. Drain off any excess grease.
Add in the drained mushrooms, tomato sauce, pizza sauce, tomato paste, and seasonings. Stir well and heat over low heat until the meat mixture is heated through. (If preparing ahead of time, skip heating it through.)
Once the pasta is cooked to al dente, drain and stir it into the meat sauce.
Add half of the mixture into the bottom of a 9x13 casserole dish. (See Note below for smaller portions.) Top the sauce with 2 cups of shredded cheese. Layer on the pepperonis, using half the package. Repeat the layers again using the rest of the meat and pasta mixture, 2 cups of shredded cheese, and the rest of the pepperonis. Top with the grated Parmesan cheese.
Cover the casserole with aluminum foil and bake in a preheated oven for 15 minutes. Remove the foil and cook an additional 10-15 minutes or until heated through and the cheese is melted.
Notes
To Make Ahead Of Time: Follow the same directions, but do not heat up the meat sauce after adding the tomato products and seasonings. Layer the ingredients as instructed. Cover the prepared casserole dish with plastic wrap and place it in your refrigerator. Remove the plastic before baking.Either allow the casserole to come to room temperature before baking, or stick the dish into the oven while it preheats. The cooking time may need to be adjusted slightly since the meat and pasta sauce aren't warm when going in the oven.To Freeze: Prepare the casserole as instructed using a freezer-safe dish. Do not heat the meat sauce after adding the tomato products and seasonings. Make sure the ingredients are completely cool before covering the container tightly in plastic wrap. Then wrap in two layers of aluminum foil. Label and freeze for up to 3 months.To cook, allow the frozen casserole to thaw in the refrigerator overnight, then bake using the "To Make Ahead Of Time" directions.