Place diced onion and chicken breast in slow cooker.
In a small bowl whisk together sauce ingredients and spices. Pour sauce over chicken. Cook on LOW for 6-7 hours or HIGH for 3-4 hours until chicken easily shreds.
Shred chicken and place back in crock-pot, turn heat to warm, remove lid and allow chicken to absorb juices for ~ 15-30 minutes.
To serve: Add additional BBQ sauce as desired, place on toasted bun.
Notes
Bourbon Substitution: A whiskey like Jack Daniel's or Worcestershire sauce.