Whisk the soy sauce, brown sugar, water, garlic, ginger, and one tablespoon of oil in a bowl. This mixture will serve as both the marinade and the base for the glaze. It should be well-combined and smooth.
Place the chicken thighs in a shallow dish and pour the marinade over them. Make sure each piece is coated well. Let them marinate for at least 30 minutes or up to a full day in the refrigerator for deeper flavor.
Heat the remaining tablespoon of oil in a skillet over medium heat. Add the chicken, discarding the leftover marinade. Cook about 5–7 minutes per side until the chicken is cooked through and the sauce in the pan reduces into a sticky glaze.
Remove the chicken from the skillet and let it rest for a few minutes to keep it juicy. Slice into strips and spoon any remaining glaze from the pan over the top before serving.