Preheat your oven to 400°F (200°C) and grease a 9x13 inch baking dish.

Cook the penne pasta in salted boiling water for 7-8 minutes until slightly under al dente. Drain and set aside.

In a skillet, heat olive oil and sauté diced onion for 2 minutes before adding ground beef. Cook for 8-10 minutes until browned.

Stir in minced garlic and cook for an additional 30 seconds.

Add marinara sauce to the skillet, season with salt and black pepper, and simmer for 1-2 minutes.

Combine the cooked penne pasta with the beef and marinara mixture in the baking dish.

Sprinkle a generous layer of cheddar cheese on top of the casserole.

Bake for about 10 minutes until the cheese is melted and golden.

Let the casserole cool for 2-3 minutes before serving.