01 - In a medium bowl, whisk together the soy sauce, honey, hoisin sauce, rice vinegar, brown sugar, sesame oil, minced garlic, grated ginger, and red pepper flakes if using. Whisk vigorously until the brown sugar completely dissolves and the mixture is well blended.
02 - Arrange the chicken drumsticks in the slow cooker, ensuring they fit comfortably without overcrowding. Pour the prepared glaze evenly over the chicken, using tongs to turn each drumstick and coat thoroughly on all sides.
03 - Cover the slow cooker with the lid. Cook on low heat setting for 4 hours or until the chicken reaches an internal temperature of 165°F and is tender enough to easily pull away from the bone.
04 - Carefully transfer the cooked drumsticks to a serving platter using tongs. Cover loosely with aluminum foil to keep warm while preparing the sauce.
05 - Pour the cooking liquid from the slow cooker into a small saucepan. In a separate small bowl, combine the cornstarch and water, stirring until smooth to create a slurry.
06 - Place the saucepan with the cooking liquid over medium-high heat. Whisk in the cornstarch slurry and bring to a boil while stirring constantly. Continue stirring for 2-3 minutes until the sauce thickens enough to coat the back of a spoon.
07 - Brush or spoon the thickened glaze generously over the chicken drumsticks, ensuring each piece is evenly coated with the glossy sauce.
08 - Sprinkle the sliced scallions and sesame seeds over the glazed drumsticks just before serving. Serve immediately while hot.