In a medium bowl, whisk together soy sauce, brown sugar, honey, garlic, and ginger until well combined. Reserve 1/2 cup of the marinade for later.
Place the chicken thighs in a large resealable plastic bag or a shallow dish and pour the remaining marinade over the chicken. Seal the bag or cover the dish and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Heat vegetable oil in a large skillet over medium-high heat. Remove chicken from the marinade and discard the marinade used for marinating.
Cook the chicken in the skillet for about 5-7 minutes on each side, or until the chicken is cooked through and has a nice golden color. The internal temperature should reach 165°F.
In a small bowl, mix cornstarch and water to create a slurry. Add the reserved marinade to the skillet and bring to a simmer. Stir in the cornstarch slurry and cook until the sauce thickens, about 2-3 minutes.
Slice the cooked chicken and return it to the skillet, tossing it in the thickened sauce to coat.
Serve the teriyaki chicken over cooked white rice and garnish with sliced green onions and sesame seeds if desired.