Preheat your oven to 400°F (200°C). Line a baking sheet with aluminum foil and place a wire rack on top.
In a large mixing bowl, combine the plum sauce, soy sauce, rice vinegar, honey, garlic powder, ground ginger, black pepper, and red pepper flakes. Mix well to create the marinade.
Add the chicken drumsticks to the bowl and toss them in the marinade until they are fully coated. Let them marinate for at least 30 minutes at room temperature or up to 2 hours in the refrigerator.
Arrange the marinated drumsticks on the wire rack, ensuring they are spaced apart for even cooking.
Bake in the preheated oven for 35-40 minutes, or until the chicken is cooked through and has a nice glaze. Baste with extra marinade halfway through for added flavor.
Once done, remove from the oven and let the drumsticks rest for 5 minutes. Garnish with chopped green onions and sesame seeds before serving.