In a medium bowl, combine the cream of mushroom soup, milk, and onion soup mix. Mix well.
Pour the soup mixture over the chicken in the crockpot.
Place the lid on the crockpot and cook the chicken for 4 to 5 hours on low.
Notes
Adding additional fresh, sliced mushrooms or canned mushrooms works well in this recipe. Please note that you may want to use less milk, water, or broth since the mushrooms will add additional liquid to the sauce and make it thinner.
Chicken broth may be substituted for the milk in this recipe.