Preheat oven to 350 degrees and grease a baking dish with nonstick cooking spray.
In a large skillet, cook the ground beef and sausage with the onion over medium heat until no longer pink. Drain and stir in the spaghetti sauce.
Cook ziti pasta according to package directions. Drain well.
In a large bowl, combine eggs, ricotta cheese, and 1 1/2 cups mozzarella cheese.
Add the pasta to cheese mixture and stir until mixed.
Spoon a third of the meat sauce into the baking dish, then top with half of the pasta mixture. Repeat layers, ending with meat sauce on top.
Cover and bake 40 minutes, then uncover and top with remaining mozzarella cheese. Bake 5-10 minutes longer or until cheese is melted.
Let stand 10 to 15 minutes before serving.