01 - In a medium bowl, whisk together soy sauce, honey, hoisin sauce, rice vinegar, brown sugar, sesame oil, garlic, ginger, and red pepper flakes until thoroughly combined and sugar dissolves.
02 - Arrange chicken drumsticks in the slow cooker insert. Pour prepared glaze over chicken, using tongs to turn pieces and ensure even coating on all sides.
03 - Cover slow cooker with lid. Cook on low setting for 4 hours until chicken reaches internal temperature of 165°F and meat is tender, nearly falling from bone.
04 - Transfer cooked drumsticks to a serving platter using tongs. Cover loosely with aluminum foil to maintain warmth while preparing sauce.
05 - Pour cooking liquid from slow cooker into small saucepan. In separate small bowl, mix cornstarch and water until smooth. Stir cornstarch mixture into saucepan and bring to boil over medium-high heat, stirring constantly for 2-3 minutes until sauce thickens and coats spoon.
06 - Brush or spoon thickened sauce generously over drumsticks. Sprinkle with sliced scallions and sesame seeds. Serve immediately with steamed rice.