Prep casserole dish & oven:
Preheat oven to 350°F (175°C) and spray a 3-quart casserole dish with non-stick spray.

Cook sausage:
Remove sausage from casing and crumble into a large skillet. Cook over medium heat until browned. Drain excess grease, reserving 2 tablespoons, and set sausage aside.

Sauté vegetables:
Add reserved grease to skillet. Sauté onion and garlic until onions are translucent.

Add tomatoes & seasonings:
Pour in diced tomatoes. Add basil, oregano, salt, and pepper. Cook over medium heat for 5 minutes.

Combine sausage & simmer:
Return sausage to skillet. Bring mixture to a boil, then cover and simmer on low for 20–30 minutes, stirring occasionally.

Cook pasta:
Prepare penne according to package directions for al dente. Drain, rinse, and return to pot.

Mix pasta & sauce:
Stir sausage mixture into pasta. Add half of the mozzarella and stir until melted.

Assemble casserole:
Place half of the pasta mixture into the prepared casserole dish. Sprinkle with cheese, then add the remaining pasta and top with remaining mozzarella.

Bake:
Cover with foil and bake 30 minutes until heated through. Remove foil and bake a few more minutes for golden, bubbly cheese.

Serve:
Slice and serve hot with salad and garlic bread.