Combine the sauce: In the crockpot, whisk together the honey, soy sauce, minced garlic, ketchup, ginger, and red pepper flakes if using.
Add the chicken: Place the chicken thighs into the crockpot and turn to coat in the sauce.
Cook: Cover and cook on low for 6 hours or high for 3 hours, until the chicken is tender and shreds easily.
Thicken the sauce: Remove the chicken to a plate. Whisk the cornstarch and water together, then stir into the sauce in the crockpot. Cook on high, uncovered, for 5-10 minutes until the sauce thickens.
Finish: Shred or slice the chicken, return it to the thickened sauce, and toss to coat. Serve over rice, topped with green onions and sesame seeds.
Notes
Servings estimated from 2 lbs of chicken thighs; adjust to taste.