01 - Preheat the oven to 375 degrees Fahrenheit. Lightly grease a 9x13-inch baking dish.
02 - Bring a large pot of salted water to a boil. Add rigatoni and cook until just al dente, about 2 minutes less than package directions. Drain and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add Italian sausage, breaking it up with a spoon, and cook until browned, about 5 to 7 minutes. Transfer cooked sausage to a plate.
04 - In the same skillet, add onion and bell peppers. Sauté until softened, about 5 minutes. Stir in minced garlic and cook for 1 minute until fragrant.
05 - Stir in tomato paste, crushed tomatoes, dried oregano, dried basil, and red pepper flakes. Season with salt and freshly ground black pepper. Bring to a simmer and cook for 10 minutes.
06 - Return cooked sausage to the skillet, mixing thoroughly into the sauce.
07 - In a large bowl, combine the cooked rigatoni with sausage and pepper sauce until well incorporated.
08 - Spread half the pasta mixture in the prepared baking dish. Sprinkle with half the mozzarella and Parmesan cheese. Top with the remaining pasta and finish with the remaining mozzarella and Parmesan.
09 - Cover loosely with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10 to 15 minutes until the casserole is bubbly and golden.
10 - Allow the casserole to rest for 5 minutes before garnishing with fresh basil or parsley. Serve warm.