01 - In a medium bowl, whisk together the soy sauce, honey, hoisin sauce, rice vinegar, brown sugar, sesame oil, garlic, ginger, and red pepper flakes (if using) until well combined and smooth.
02 - Place the chicken drumsticks in the slow cooker. Pour the prepared glaze over the chicken, turning drumsticks to coat evenly on all sides.
03 - Cover and cook on low setting for 4 hours or until the chicken is cooked through and tender, reaching an internal temperature of 165°F.
04 - Transfer the drumsticks to a serving platter and cover loosely with aluminum foil to keep warm while preparing the sauce.
05 - Pour the cooking liquid into a small saucepan. In a separate small bowl, mix cornstarch and water to form a smooth slurry. Stir the slurry into the cooking liquid.
06 - Bring the sauce to a boil over medium-high heat, stirring constantly until thickened and glossy, approximately 2-3 minutes.
07 - Brush or spoon the thickened glaze generously over the drumsticks. Garnish with sliced scallions and sesame seeds immediately before serving.