Spray CrockPot with cooking spray, or use a liner for easy clean-up.
Rinse Chicken thighs and remove excess skin; place in CrockPot. Cover thighs with sliced onion pieces
In a large mixing bowl, combine honey, ketchup, soy sauce and minced garlic; stir well.
Pour sauce over chicken and onions; sprinkle pepper over top if desired.
Place lid on CrockPot and cook on LOW 6-8 hours or HIGH 4-6 hours, until thighs test done.
To thicken the sauce, combine water and cornstarch and add to CrockPot at end of cooking time. Stir well and cook on HIGH for 15 minutes. Stir and serve.