Mix Soy Sauce (2 teaspoon), Worcestershire Sauce (2 teaspoon), Ketchup (1 tablespoon) and Brown Sugar (2 teaspoon) in a small bowl.
Pour Marinade (to taste) over the Boneless, Skinless Chicken Thigh (4 piece) and gently massage it into the chicken.
Let the chicken marinade in the fridge for at least 2 hours and up to overnight.
Grill or pan-fry the chicken over medium-high heat for about 2 minutes on each side or until fully cooked. Set aside.
In a small bowl, mix 1 teaspoon of Sweet Soy Sauce (1 teaspoon), Worcestershire Sauce (1 teaspoon), Brown Sugar (1 teaspoon), Ground Black Pepper (1/2 teaspoon), Salt (1/4 teaspoon), Corn Starch (1 teaspoon) and Water (3 tablespoon). Stir well until combined.
Melt Butter (1 tablespoon) in a pan over medium-low heat, then add Olive Oil (2 teaspoon).
Add Onion (1/2) and Garlic (2 clove). Saute until the onions are soft and translucent.
Add the black pepper sauce mixture, then turn up the heat. Let the sauce simmer for just a minute. This will allow it to thicken up.
Pour the sauce over the chicken, then serve right away. Enjoy!