01 - Whisk together soy sauce, honey, hoisin sauce, rice vinegar, brown sugar, sesame oil, minced garlic, grated ginger, and red pepper flakes (if using) in a medium bowl until completely smooth and well combined.
02 - Arrange chicken drumsticks in the slow cooker insert. Pour the prepared glaze over the chicken, using tongs to turn each piece and ensure even coating on all sides.
03 - Cover and cook on low setting for 4 hours, or until chicken reaches internal temperature of 165°F and meat is tender enough to pull easily from the bone.
04 - Transfer cooked drumsticks to a serving platter using tongs and cover loosely with aluminum foil to maintain warmth while finishing the sauce.
05 - Pour cooking liquid from slow cooker into a small saucepan. Combine cornstarch and water in a separate cup to create a smooth slurry, then stir into the hot liquid.
06 - Bring sauce mixture to a boil over medium-high heat, stirring constantly for 2-3 minutes until glaze thickens enough to coat the back of a spoon.
07 - Brush or spoon the thickened glaze generously over each chicken drumstick, ensuring an even coating of the reduced sauce.
08 - Sprinkle sliced scallions and sesame seeds over the glazed chicken just before serving.