Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Cook ziti pasta according to package instructions. Drain and set aside.
In a large skillet over medium heat, sauté onion until soft. Add garlic and cook for 1 minute.
Add ground beef and sausage to the skillet. Cook until browned. Drain excess fat.
Stir in marinara sauce, tomato sauce, Italian seasoning, salt, and pepper. Simmer for 10 minutes.
In a large bowl, mix ricotta cheese, egg, and half the Parmesan cheese until combined.
Add cooked pasta and half of the meat sauce to the ricotta mixture. Stir until well coated.
Spread half the pasta mixture in the baking dish. Layer with half of the mozzarella cheese.
Repeat with remaining pasta mixture and meat sauce. Top with remaining mozzarella and Parmesan cheese.
Cover with foil and bake for 20 minutes. Uncover and bake for another 10–15 minutes until bubbly and golden.
Let rest for 5–10 minutes before serving. Garnish with fresh parsley.