Preheat oven to 375. Prepare a 2-quart casserole dish with cooking spray; set aside. In a mixing bowl, combine vegetables, cooked chicken, and cornbread mixes. Mix well. Pour into prepared dish. In another mixing bowl, combine milk, egg whites, and black pepper. Mix well. Pour over chicken mixture. Bake, covered, for 45 minutes. Top with cheese and bake, uncovered for three minutes or until cheese has melted.