Sprinkle chicken breasts generously with salt and pepper and then give both sides a generous dousing of liquid smoke (I did 2-3 squirts on each side of the chicken breast). Place chicken breasts inside of slow cooker.
In a bowl, mix together mustard, honey, and garlic. Pour of the top of the chicken breasts and place lid on top of slow cooker.
Cook on LOW for 5-6 hours or HIGH 3-4 hours (but I highly recommend cooking on low).
Remove chicken from slow cooker and serve.
Notes
When I am short on time, I will substitute this Honey Mustard Dressing instead of making my own. It still turns out awesome!