Place ¼ cup water in a bowl (or in a two cup measuring cup). Add the can of cream of chicken soup. Stir well. Set aside.
Coat a 9 x 13 glass pan with cooking spray. Place four chicken breasts in the pan. Place a slice of Swiss cheese on each chicken breast. Pour the cream of chicken soup mixture evenly over the chicken breasts. Spread the stuffing mix evenly on top. Slice the butter into small pieces and scatter over the top of the stuffing.
Place the pan in the preheated oven and bake for 30-45 minutes, depending on the thickness of the chicken breasts. They are done when a meat thermometer reads 165°. Remove from the oven and let rest for five minutes before serving.