Season the chicken. Pat the thighs dry.
Sprinkle both sides with a pinch of salt and pepper. This builds flavor from the start.
Make the sauce. In a small bowl, whisk honey, soy sauce, chicken broth, minced garlic, vinegar, sesame oil, ginger, and red pepper flakes. Taste and adjust—add a bit more honey for sweetness or vinegar for brightness.
Load the slow cooker. Place chicken thighs in the slow cooker in an even layer.
Pour the sauce over the top, making sure all pieces are coated.
Cook low and slow. Cover and cook on Low for 4–5 hours or on High for 2.5–3 hours, until the chicken is tender and reaches 165°F (74°C).
Thicken the sauce. Transfer the chicken to a plate. Whisk cornstarch and cold water into a slurry. Stir it into the cooking liquid.
Cover and cook on High for 10–15 minutes until thick and glossy. (Or simmer the sauce in a small pot on the stove.)
Finish and serve. Return chicken to the slow cooker and toss in the sauce. Garnish with sesame seeds and green onions. Serve over rice, cauliflower rice, noodles, or mashed potatoes with a side of steamed broccoli.