1. Preheat the oven to 375°F and lightly grease a 9×13-inch baking dish.

2. Bring a large pot of salted water to a boil and cook the ziti until just al dente. Drain and set aside.

3. Heat the olive oil in a large skillet over medium heat. Add the ground beef and diced onion, then cook until the beef is browned and the onion is soft. Drain excess grease if needed.

4. Stir in the garlic, Italian seasoning, salt, and black pepper. Cook for 30 seconds.

5. Add the marinara sauce and simmer for 5 to 7 minutes.

6. In a medium bowl, mix the ricotta cheese, egg, Parmesan cheese, 1 cup of the mozzarella, and chopped parsley until well combined.

7. Spread a thin layer of meat sauce in the bottom of the prepared baking dish.

8. Add half of the cooked ziti, half of the ricotta mixture, and half of the remaining sauce. Repeat with the remaining ziti, ricotta mixture, and sauce.

9. Sprinkle the remaining 2 cups mozzarella evenly over the top.

10. Bake uncovered for 25 to 30 minutes, until hot and bubbly.

11. Broil for 1 to 2 minutes if you want a more golden cheese topping.

12. Let the baked ziti rest for 10 minutes before serving.