Preheat your oven to 375°F (190°C).

Cook the ziti pasta according to package instructions until al dente. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute.

Add the ground beef or Italian sausage to the skillet. Cook until browned, breaking it apart with a spoon, about 7-10 minutes. Drain any excess fat.

Pour in the marinara sauce, and stir to combine. Allow the mixture to simmer for about 5 minutes.

In a large bowl, mix together the ricotta cheese, egg, dried oregano, salt, and black pepper until well combined.

In a large baking dish, spread a thin layer of the meat sauce on the bottom. Add half of the cooked ziti, followed by half of the ricotta mixture, and then half of the mozzarella cheese. Repeat the layers with the remaining ingredients, finishing with the remaining mozzarella and Parmesan cheese on top.

Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.

Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown.

Remove from the oven and let it cool for a few minutes. Garnish with fresh basil or parsley if desired, and serve warm.