Preheat oven to 375°F (190°C) and lightly grease a 9x13-inch baking dish.

Cook the penne pasta in a large pot of salted boiling water until 1 minute shy of al dente. Drain and set aside.

Heat olive oil in a large skillet over medium-high heat. Add the diced onion and cook until softened, about 3 to 4 minutes.

Add the ground beef to the skillet, breaking it apart with a wooden spoon. Cook until browned, about 5 to 7 minutes. Drain any excess fat.

Stir in the minced garlic, Italian seasoning, salt, and black pepper. Cook for 1 minute until fragrant.

Pour the tomato sauce into the skillet with the beef and simmer on low heat for 10 minutes.

Combine the cooked penne pasta and the beef meat sauce in the prepared baking dish, tossing well to coat.

Sprinkle the mozzarella cheese evenly over the top of the pasta and beef mixture.

Bake uncovered for 15 to 20 minutes, or until the cheese is melted and bubbly.

Garnish with freshly chopped parsley before serving.