In a small saucepan over medium-high heat, whisk together 1 tablespoon sesame oil and 1 tablespoon cornstarch.
Stir in 1/2 cup soy sauce, 1/2 cup rice vinegar, 3/4 cup brown sugar, 6 cloves minced garlic, 1 teaspoon ground ginger, 1 teaspoon sesame seeds, and 1/2 teaspoon crushed red pepper flakes.
Bring to a simmer and cook, stirring occasionally, for 3 to 5 minutes or until thickened and glossy. Remove from heat.
Lightly coat a 9x13-inch baking dish (or large baking sheet) with nonstick cooking spray. Arrange 8 chicken drumsticks in a single layer.
Brush the drumsticks generously with the sauce, reserving some for basting later.
Bake in the preheated oven for 45 minutes, basting with the remaining sauce halfway through. Chicken is done when it reaches an internal temperature of 165℉ (74℃).
Remove from oven and transfer to a serving platter. Garnish with 2 tablespoons sliced green onion and 1 teaspoon sesame seeds.
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Notes
Serve hot, optionally with steamed rice or stir-fried vegetables. Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.