Cook ground beef and onion in a large skillet over medium high heat, stirring occasionally, until no longer pink. Stir in seasonings to evenly coat meat,stir in pasta sauce set aside.
Mix 1 cup mozzarella, ricotta, and parmesan in a bowl. Spoon 2 cups of meat sauce into the slow cooker and top with 2 cup ziti. Drop 1/2 of cheese mixture over ziti and spread over ziti. Layer with 2 cups of meat sauce, the remaining ziti and remaining cheese. Add meat sauce and place lid on slow cooker.
Cook on low for 6-7 hours or on high for 4-5 hours.
Sprinkle food with remaining cup of mozzerella and let stand for 10 minutes until melted.