In a mixing bowl, whisk together the low-sodium soy sauce, water, brown sugar, rice vinegar, grated ginger, minced garlic, sesame oil, and Sriracha to create a flavorful marinade.
Place the chicken drumsticks in a large resealable bag or a shallow dish. Pour the marinade over the drumsticks, ensuring they are well coated. Seal the bag or cover the dish and refrigerate for at least 1 hour, or up to overnight for maximum flavor.
Preheat your oven to 425°F (220°C). This high temperature will help achieve that crispy skin we all love.
Line a baking sheet with parchment paper for easy clean-up. Arrange the marinated drumsticks on the sheet, shaking off any excess marinade. Reserve the leftover marinade for later use. Bake in the preheated oven for 25-30 minutes.
While the chicken is baking, pour the reserved marinade into a saucepan. Bring it to a boil over medium heat, then stir in the cornstarch mixed with water. Continue to cook until the sauce thickens, about 2-3 minutes.
After 25-30 minutes, remove the drumsticks from the oven. Brush the thickened teriyaki sauce over each drumstick, then return them to the oven. Bake for an additional 10-15 minutes, or until the chicken is cooked through and the skin is crispy.
Once done, let the chicken rest for a few minutes. Serve the Baked Teriyaki Chicken Drumsticks hot, garnished with sliced green onions and sesame seeds for an extra touch.