1. In slow cooker combine the soup, onion, parsley, wine, garlic powder, milk, mushroom pieces, salt and pepper. Mix together, then place chicken on top of mixture. Spoon some of the sauce over the chicken.
2. Cook on Low setting for 5 to 6 hours, or on High setting for 3 to 4 hours. (Note: You may use frozen chicken breasts directly; just add another 1 to 1-1/2 hours cooking time.)