Cook the Pasta:
Bring a large pot of salted water to a boil. Add pasta and cook until al dente, according to package instructions. Drain and set aside.

Prepare the Meat Sauce:
In a large skillet over medium heat, cook the ground beef or Italian sausage until browned. Add the chopped onion, bell pepper, and garlic, and sauté until the vegetables are tender. Drain any excess fat. Stir in the pizza sauce, Italian seasoning, salt, and black pepper. Simmer for 5 minutes.

Combine Pasta and Sauce:
In a large mixing bowl, combine the cooked pasta with the meat sauce, ensuring the pasta is evenly coated.

Assemble the Casserole:
Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking dish. Spread half of the pasta mixture into the prepared dish. Sprinkle with 1 cup of shredded mozzarella cheese and half of the sliced pepperoni. Layer the remaining pasta mixture on top and sprinkle with the remaining mozzarella cheese, pepperoni slices, and grated Parmesan cheese. Add any optional toppings as desired.

Bake:
Cover the dish with aluminum foil and bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.

Serve:
Remove from the oven and let the casserole sit for 5 minutes before serving. Enjoy with a side salad or garlic bread.