In a large saucepan, melt the butter/margarine. Add the soup, water and milk. Stir together over medium heat. Add the onion, salt and pepper and bring all to a boil.
When mixture starts boiling, add the chicken meat and simmer all together until chicken is cooked through. Add the sliced mushrooms and boil over medium heat for about 5 minutes, stirring often. Serve!
*I used chicken thighs cooked in george foreman grill for a few mins to brown then added chicken to the recipe when it says to add. Serve w/warm rolls.