In a medium bowl, whisk together the soy sauce, honey, rice vinegar, sesame oil, minced garlic, and grated ginger until well combined. This will be the teriyaki marinade.
Place the chicken thighs in a resealable plastic bag or a shallow dish and pour the teriyaki marinade over them. Seal the bag or cover the dish, and refrigerate for at least 30 minutes, preferably 2-3 hours for deeper flavor.
Preheat your oven to 400°F (200°C).
Remove the chicken thighs from the marinade, reserving the marinade for later. Place the chicken thighs skin-side up on a baking sheet lined with parchment paper.
In a small saucepan over medium heat, pour in the reserved marinade. Bring to a gentle simmer and cook for about 3-4 minutes, allowing it to thicken slightly.
In a small bowl, mix the cornstarch with water to create a slurry, and then add this to the simmering marinade. Stir continuously until the sauce thickens, about 1-2 more minutes.
Brush the thickened sauce over the chicken thighs, reserving some for later basting.
Bake the chicken thighs in the preheated oven for about 35-40 minutes, basting with the reserved sauce halfway through cooking, until the chicken juices run clear and the skin is crispy.
Once cooked, remove the chicken from the oven and let it rest for 5 minutes.
Garnish with sesame seeds and sliced green onions before serving with steamed rice or vegetables.
Notes
For best flavor, marinate the chicken for 2-3 hours.