Line a 3-1/2 or 4-quart slow cooker with a disposable slow cooker liner. Lightly coat liner with cooking spray; set cooker aside. In a very large bowl stir together soup, butter, and water. Add frozen vegetables, chicken, and stuffing mix; stir until combined. Transfer mixture to the prepared slow cooker.
Cover and cook on low-heat setting for 5 to 6 hours or on high-heat setting for 2-1/2 to 3 hours. Makes 6 servings.