Preheat the oven to 375°F (190°C).
Cook the rigatoni pasta according to package instructions until al dente.
In a large skillet, sauté the diced onion and minced garlic until softened.
Add the ground beef to the skillet, breaking it apart and cooking until browned.
Stir in the marinara sauce, oregano, salt, and pepper, allowing it to simmer for about 10 minutes.
Combine the cooked rigatoni with the beef ragu in the skillet, mixing well.
Transfer the mixture to a greased baking dish, layering half of the mozzarella cheese on top.
Spread the remaining mozzarella and Parmesan cheese on top.
Cover the baking dish with foil and bake for 25 minutes, then remove the foil and bake for an additional 15 minutes.
Allow the baked rigatoni to rest for 10 minutes before serving.
