In a bowl, whisk together the soy sauce, brown sugar, water garlic, onion, ginger, oregano and pepper.
Place the chicken in a 12-inch skillet. Pour the sauce mixture over the chicken and turn the stove to medium heat. Bring the mixture to a boil, then reduce to a simmer.
Cook the chicken, turning over once halfway through the cook time, until the chicken is cooked through, about 20 minutes.
When the chicken is done, remove it to a plate.
In a small bowl, combine the cornstarch with about 1 tablespoon of water, then add the cornstarch slurry to the sauce in the skillet. Whisk to combine and cook until slightly thickened.
Return the chicken to the skillet and turn the chicken to coat in the sauce.
Serve over rice, if desired.
