Cook pasta shells according to directions. Drain and rinse in cold water, being careful not to tear the shells. Mix browned chicken, ricotta, onions, bread crumbs, eggs, seasonings, and about a quarter-cup of the spaghetti sauce in a large bowl. Line a 9x13 pan with a layer of spaghetti sauce. Stuff the shells with at least a heaping dinner-tablespoon-full of the chicken mixture. There's a lot of the mixture, so don't be afraid to stuff them well. Place the shells in the pan and top with as much spaghetti sauce as you like. (You have to use at least enough to cover the shells.) Cover the pan with aluminum foil and bake at 350 degrees for 45 mins. (If you make the shells ahead of time and store them in the refrigerator, you will need to bake them for about 1 hour and 15 mins.) During the last 10 minutes of baking, top with the mozzarella cheese.

*I hate working with onions, so I prefer to used dried. If you're an onion purist, you may want to saute some fresh minced onions with the chicken.