Prepare stuffing mixes according to package directions. Meanwhile, in a large bowl, combine soup and milk; set aside. Spread the stuffing into two greased 8-in. square baking dishes. Layer with chicken, corn, mushrooms, soup mixture and cheese.
Cover and freeze one casserole for up to 3 months. Cover and bake the second casserole at 350° for 30-35 minutes or until cheese is melted.
To use frozen casserole: Remove from the freezer 30 minutes before baking (do not thaw). Bake at 350° for 1-1/2 hours. Uncover; bake 10-15 minutes longer or until heated through. Yield: 2 casseroles (6 servings each).