Preheat the oven to 425°F (220°C) and lightly spray a 9×13-inch baking pan with nonstick spray.
Arrange the 8 drumsticks in the baking pan, skin side down in a single layer.
In a mixing bowl, whisk together 1/4 cup low-sodium soy sauce, 1/4 cup water, 3 tablespoons brown sugar, 2 tablespoons rice vinegar, 1 tablespoon grated fresh ginger, 3 cloves minced garlic, 1 teaspoon sesame oil, and 1–3 teaspoons Sriracha until the sugar dissolves.
Pour the sauce over the drumsticks, coating them evenly.
Bake the drumsticks for 40–45 minutes, flipping once halfway through, until the internal temperature reaches 165°F (74°C) and the skin is mostly cooked.
Transfer the pan sauce to a saucepan and bring it to a simmer over medium heat.
Stir the cornstarch slurry (1 tablespoon cornstarch mixed with 1 tablespoon water) and whisk it into the simmering sauce. Return to a gentle simmer and cook until the sauce thickens and becomes glossy.
Brush the thickened sauce liberally over the drumsticks, then place the pan under the broiler for 2–5 minutes until the glaze is browned and sticky—watch closely to prevent burning.
Garnish with sliced green onions and sesame seeds before serving.
