Prepare the stuffing per directions on package. (I always put chopped Onion and celery in my stuffing, and this adds some nice texture to this dish if you want)
Mix soup and Milk in a 9x13 baking dish sprayed with cooking spray. Stir in meatballs and peas (if you are adding peas) and top with Stuffing and Cheese.
Bake, uncovered 20-25 minutes.
* To Make ahead* Prepare and bake as directed, cool completely, wrap tightly and freeze up to one month. When ready to serve, thaw frozen casserole overnight, then bake (covered) for 25 minutes.
** Variation ** Prepare as above, but omit the milk. Use Italian Meatballs and substitute 1 can Diced Tomatoes for the can of Mushroom soup, then substitute mozzarella for the cheddar cheese.