1(26oz) jar prepared spaghetti sauce (If you like it saucier use more)
Cook shells according to package directions. Be careful not to overcook them or they will tear easily when trying to fill them. Drain and set shells out individually on a cutting board or baking sheet so that they don’t stick together.
Preheat oven to 350°. Lightly grease two 9x13 baking dishes.
In a large bowl, combine chicken and all the rest of the ingredients except mozzarella and spaghetti sauce. Stir in 1 cup mozzarella. Spoon into shells. *Tip: For easier filling, fill a gallon ziplock baggie with the filling and snip a quarter size hole off the corner of the bag. Then you can just pipe the filling into the 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. If you are freezing one of the 9x13 prepared pans, freeze it after this step. Include a baggy of the remaining mozzarella for when you cook it.
Bake, covered, for 40 minutes. Uncover, sprinkle with remaining 1 cup mozzarella. Bake for 5 to 10 more minutes.