Prepare the Marinade: Whisk together soy sauce, dark brown sugar, rice wine vinegar, honey, minced garlic, sesame oil, ground ginger, and ground black pepper in a mixing bowl.

Marinate the Chicken: Place cut chicken thighs in a resealable bag or bowl, pour marinade over them, ensuring all pieces are coated. Marinate in the refrigerator for at least 30 minutes.

Cook the Chicken: Heat vegetable oil in a large skillet over medium-high heat. Add marinated chicken pieces in a single layer and sauté for 5-7 minutes until cooked through and golden-brown.

Thicken the Sauce: Mix cornstarch with cold water to create a slurry. Pour it into the skillet with the chicken during the last minute of cooking, stirring continuously until the sauce thickens.

Serve and Garnish: Transfer chicken teriyaki to a serving dish, garnish with sliced green onions and sesame seeds. Serve over steamed rice with broccoli or seasonal veggies.