Chicken and Spinach Stuffed Shells

22 uncooked jumbo pasta shells
1 c chopped cooked chicken
1 c fresh chopped spinach
1/2 onion, chopped
2 cloves garlic, minced
1/2 (15oz) container ricotta cheese
1 (8oz) package cream cheese, softened
1 c shredded Parmesan cheese
1 large egg, lightly beaten
2 tsp dried parsley flakes
1/2 tsp Italian seasoning
1/4 tsp salt
1/4 tsp pepper
1 c shredded mozzarella cheese, divided
1/2 (26oz) jar prepared spaghetti sauce (any variety)

Cook shells according to package directions (be sure to stir every once in awhile so they don't stick to the bottom of the pan and tear apart); drain and set aside.
Preheat oven to 350°. Lightly grease 13x9x2inch baking dish.
In a large bowl, combine chicken and all the rest of the ingredients except mozzarella and spaghetti sauce. Stir in 1/2 cup mozzarella. Spoon into shells. Spread half of spaghetti sauce into prepared baking dishes. Arrange shells over sauce; top with remaining sauce. Cover tightly with heavy-duty aluminum foil. Bake, covered, for 40 minutes. Uncover, sprinkle with remaining 1/2 cup mozzarella. Bake for 5 to 10 more minutes.
Makes 6-8 servings.