Creating Pizza Casserole is straightforward if you follow these easy steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a 9×13 inch baking dish.
2. Cook Pasta: Boil the pasta according to package instructions until al dente. Drain and set aside.
3. Cook Meat: In a skillet over medium heat, cook the ground beef or sausage until browned, breaking it apart as it cooks. Drain excess fat if necessary.
4. Add Vegetables: Add the diced onion and bell pepper to the skillet with the meat. Cook until the vegetables are tender, about 3-4 minutes.
5. Mix Ingredients: In a large bowl, combine the cooked pasta, meat mixture, marinara sauce, Italian seasoning, salt, and pepper. Stir until everything is well combined.
6. Layer the Casserole: Pour half of the pasta mixture into the greased baking dish. Sprinkle with half of the mozzarella and Parmesan cheese. Layer pepperoni on top, if using, then add the remaining pasta mixture and top with the rest of the cheeses.
7. Bake: Cover with aluminum foil (to prevent burning) and bake for 20 minutes. Remove the foil and bake for an additional 10-15 minutes or until the cheese is bubbly and golden.
8. Cool and Serve: Once out of the oven, let the casserole cool for a few minutes before slicing into square portions.