Using a mallet or meat tenderizer, pound the chicken breasts until the meat is flat and even.
Season the chicken with salt and pepper.
Add a layer of spinach and a slice of Swiss cheese. Roll each breast tightly to ensure that the filling can not escape.
Wrap each breast tightly in aluminum foil.
In a deep pan, bring the water to a boil.
Place the foil-wrapped breasts into the water. Use a heat-proof plate to weigh the chicken breasts down and keep them completely submerged in the water.
Allow them to simmer in the water for 20-25 minutes, or until the chicken is completely done.