Spray the body of a 6 or 8-quart slow cooker with cooking spray.
Add the chicken breasts to the bottom of the slow cooker.
Sprinkle the brown sugar, garlic powder, onion powder, cayenne, and salt all over the chicken.
Add the slices of butter on top.
Cook for 5-6 hours on low or 3-4 hours on high.
Shred the chicken with two forks in the slow cooker and mix with the juices. Keep warm while you make the sauce.
In a small saucepot, add the butter, brown sugar, cayenne, garlic powder, onion powder, and salt.
Place over medium heat and stir constantly so it doesn’t burn, until it comes to a simmer. Take off the heat.
Add the chicken on top of bread of your choice and drizzle the sauce on top, serve immediately.