Preheat your oven to 375 degrees Fahrenheit (190 degrees Celsius).
Brown the ground beef and Italian sausage in a large skillet over medium heat.
Add the diced onion and minced garlic to the skillet and cook until soft.
Stir in the crushed tomatoes and season with salt and pepper; let it simmer.
In a large pot of boiling salted water, cook ziti until it's slightly underdone, then drain.
In a separate bowl, combine the ricotta cheese, 2 cups of mozzarella, Parmesan, eggs, and parsley.
Layer some of the tomato-meat sauce in the bottom of a baking dish.
Next, layer half the pasta, then the cheese mixture, and repeat the layers, ending with a generous topping of mozzarella.
Bake in the preheated oven for about 20 minutes, until the cheese is bubbly and golden.