Preheat the oven to 375 degrees. Cook the penne in a large pot of salted boiling water until al dente, then drain and set aside.

Heat the olive oil in a large skillet over medium heat. Add the Italian sausage and cook until browned, breaking it into crumbles with a spoon.

Add the sliced onion and bell peppers to the skillet. Cook for 5 minutes until the vegetables soften.

Stir in the minced garlic and Italian seasoning. Cook for 1 minute more.

Pour the marinara sauce into the skillet and season with salt and black pepper. Simmer for 3 minutes, then remove from heat.

Combine the cooked penne with the sausage mixture in a large bowl. Stir in half the mozzarella and half the Parmesan.

Transfer the mixture to a greased 9x13 baking dish. Sprinkle the remaining mozzarella and Parmesan evenly over the top.

Bake for 20 minutes until the cheese is melted and lightly browned. Let it rest for 5 minutes before serving.