Reheat the pan over high heat, and cook the marinated meat, loosening the meat and flipping them over once or twice. Transfer to another plate. If using cooked bulgogi, simply heat it up in the pan.
Reduce the heat to medium high, and add a couple of teaspoons of cooking oil to the pan. Stir fry the kimchi and optional onion slices until the kimchi turns slightly soft and deep in color.