Preheat the Oven:

o Preheat your oven to 375°F (190°C).

o Gently coat a baking dish with cooking spray or cover it with parchment paper for hassle-free cleanup.

Prepare the Sauce:

o In a medium bowl, whisk together the minced garlic, grated onion, soy sauce, ketchup, honey, red pepper flakes, rice wine vinegar, and brown sugar until well combined.

Marinate the Chicken:

o Place the chicken thighs in a large zip-lock bag or a shallow dish. Pour about half of the prepared sauce over the chicken, making sure each piece is well coated. Let the chicken marinate for at least 30 minutes in the refrigerator, or up to 2 hours for more flavor.

Bake the Chicken:

o Arrange the marinated chicken thighs in the prepared baking dish, skin-side up.

o Bake in the preheated oven for 35-40 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the skin is crispy and caramelized.

Prepare the Sauce on the Side:

o While the chicken is baking, pour the drippings from the baking dish into a small saucepan. Skim off any excess fat.

o In a small bowl, mix the cornstarch with 2 tablespoons of water to make a slurry.

o Add the slurry to the saucepan and bring it to a simmer over medium heat, whisking constantly until the sauce thickens, about 1-2 minutes.

Serve:

o Once the chicken is cooked, remove it from the oven and let it rest for a few minutes.

o Serve the chicken with the thickened sauce on the side, garnished with chopped green onions or sesame seeds if desired.