Combine all ingredients except half of the onions in a slow cooker.
Cover and cook on Low for 5-6 hours. Top with remaining fried onions to serve.
Notes
Feel free to mix and match Cream of Mushroom, Cream of Celery or Cream of Chicken soups.Caution: I do not recommend using the gluten-free version of Campbell's Cream of Chicken for this recipe. The gluten-free version is a lot thinner and creates a very soupy casserole.