Prep the Chicken: Preheat oven to 400°F (200°C) and lightly grease a 9x13 inch baking dish. Pat chicken thighs completely dry with paper towels. Season both sides generously with salt and pepper. For extra crispy edges, lightly dust with cornstarch.
Make the Teriyaki Sauce: In a medium bowl, whisk together soy sauce, honey, mirin, rice vinegar, minced garlic, and grated ginger until honey dissolves completely. Reserve 1/4 cup of sauce for basting later.
Arrange and Coat: Place chicken pieces in the prepared baking dish in a single layer. Pour the teriyaki sauce over chicken, ensuring each piece is well-coated. Avoid overcrowding the pan for even cooking.
Bake: Bake for 20-25 minutes, basting halfway through with pan juices. Chicken is done when internal temperature reaches 165°F. For deeper caramelization, broil for 2-3 minutes at the end.
Thicken the Sauce: Remove baking dish from oven. Pour pan juices into a small saucepan, bring to a simmer over medium heat, and whisk in cornstarch slurry (1 tablespoon cornstarch mixed with 2 tablespoons water). Cook 2-3 minutes until glossy and thickened.
Final Glaze: Pour thickened sauce back over chicken. Brush reserved sauce over each piece for extra flavor and shine.
Garnish and Serve: Sprinkle with sesame seeds and sliced green onions. Let rest 3-4 minutes before serving. Serve over steamed rice, cauliflower rice, or noodles with your favorite vegetables.