01 - Place the chicken breasts in an even layer across the bottom of the slow cooker.
02 - In a medium bowl, whisk together the honey, soy sauce, ketchup, hoisin sauce (if using), minced garlic, grated ginger, vinegar, black pepper, and red pepper flakes until well combined.
03 - Pour the sauce mixture evenly over the chicken breasts, ensuring they are fully submerged.
04 - Cover and cook on High for 4 hours or on Low for 6 to 7 hours, until the chicken is tender and cooked through to an internal temperature of 165°F.
05 - Remove the chicken from the slow cooker and transfer to a plate. Shred using two forks, or leave the breasts whole according to preference.
06 - In a small bowl, stir together the cornstarch and cold water to form a slurry. Pour the slurry into the sauce remaining in the slow cooker and stir to incorporate.
07 - Return the shredded or whole chicken to the slow cooker. Stir to coat evenly, cover, and cook on High for an additional 15 to 20 minutes until the sauce has thickened.
08 - Serve hot over cooked rice, quinoa, or steamed vegetables. Garnish with chopped fresh parsley or green onions.