Brown the ground beef or sausage with the onion in a nonstick skillet, breaking the meat apart as it cooks.
Add the garlic, seasonings, pasta sauce, and tomato sauce and set aside.
In a medium bowl, stir together the ricotta cheese, egg, basil, Parmesan cheese, and 1 cup of shredded mozzarella cheese.
Pour ⅓ of the sauce into the bottom of a greased 6-quart slow cooker.
Scatter ⅓ of the uncooked ziti on top followed by ½ of the ricotta cheese mixture.
Repeat with another layer of sauce, ziti, and all of the remaining ricotta mixture.
Top with remaining ziti and sauce.
Cover and cook on HIGH for 2 ½ hours or on LOW for 4 to 6 hours.
Remove the lid and sprinkle the remaining mozzarella cheese on top.
Cover just long enough to melt the cheese.
Leftovers will keep in the refrigerator for 4 to 5 days.
