01 - In a large mixing bowl, whisk together soy sauce, mirin, honey, brown sugar, rice vinegar, minced garlic, grated ginger, and sesame oil until well combined.
02 - Add the chicken thighs to the bowl, turning each piece to coat evenly. Cover and refrigerate for at least 30 minutes, or up to overnight for deeper flavor penetration.
03 - Preheat the oven to 400°F. Line a baking tray with parchment paper or aluminum foil for easy cleanup.
04 - Remove the thighs from the marinade, reserving all remaining liquid. Place the chicken skin-side up on the prepared baking tray, spacing pieces evenly.
05 - Roast the chicken for 35 to 40 minutes. After the first 20 minutes, baste generously with the reserved marinade. Continue roasting until the internal temperature reaches 165°F and the skin is golden and caramelized.
06 - While the chicken roasts, pour the remaining marinade into a small saucepan and bring to a boil. For a thicker glaze, dissolve the cornstarch in water and whisk it into the sauce. Simmer for 3 to 5 minutes until glossy and coat the back of a spoon.
07 - Arrange the roasted chicken on a serving platter. Drizzle with the reduced teriyaki sauce and garnish with sliced green onions and toasted sesame seeds. Serve immediately while hot.