Heat the oil in a wok or large skillet over medium heat. Add the garlic, and cook for a few seconds until aromatic and lightly browned. Stir in the cabbage until all the pieces are thoroughly coated in oil before covering the pan. Let cook, undisturbed, for 1 minute.
Sprinkle in the soy sauce, sesame oil, sugar (if using), red pepper flakes (if using), salt and black pepper all at once, increasing the heat to high, and cook until the cabbage is tender; 2 - 4 minutes. Serve immediately.
