Place layers of green peppers, onions, cheese, and potatoes with a sprinkling of salt in slow cooker. Sprinkle salt over chicken breasts and lay on top of potatoes. Combine soup and milk and pour into slow cooker, pushing meat down into liquid. Cover. Cook on high 1 1/2 hours. Reduce temperature to low and cook 3-4 hours. Test that potatoes are soft. If not, continue cooking on low another hour and test again. Continue until potatoes are soft.