Spray slow cooker with non-stick cooking spray and place chicken inside.

Pour bottle of Kung Pao sauce on top and cook on low for 5-6 hours or high 3-4 hours. For the last 30 minutes of cooking, turn the slow cooker to high (if it isn't on high already) and add diced bell peppers, water chestnuts, and peanuts.

After finished cooking, remove chicken breasts and cut into bite-sized pieces. Return chicken to slow cooker and stir until chicken is completely covered in sauce.

Serve over white or brown rice if desired.