In a medium bowl, stir together honey, soy sauce, ketchup, hoisin sauce, ginger, garlic, onions, celery, red bell peppers, and red pepper flakes. Place chicken breasts in the bottom of the crock-pot and pour the sauce all over the top. Cover and cook on low setting for about 4-4 ½ hours or cook for 2-2 ½ hours on high setting until the chicken is cooked through and tender. *Note: Cook times vary depending on your crock-pot. This recipe only took 2 hours on high heat in my crockpot to fully cook. Make sure to check for doneness and be prepared to cook longer, if necessary!