Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch casserole dish with cooking spray.
In a medium bowl or saucepan, prepare the Stove Top stuffing according to the package directions using the hot water and butter. Fluff with a fork and set aside.
Arrange the boneless, skinless chicken breasts in a single layer at the bottom of the prepared casserole dish.
Spoon the cream of chicken soup evenly over the chicken breasts, ensuring they are fully covered.
Sprinkle the dry onion soup mix evenly over the layer of cream of chicken soup.
Top the casserole with the prepared stuffing mixture, spreading it out to cover the chicken and sauce.
Cover the dish tightly with aluminum foil and bake in the preheated oven for 45 to 60 minutes. (Check at 45 minutes if chicken breasts are thin).
Remove the foil and bake for an additional 15 minutes, or until the stuffing is golden brown and crispy and the chicken reaches an internal temperature of 165°F (74°C).
Let the dish rest for 5 minutes before serving to allow the sauce to set slightly.