Heat the wok over a high heat until smoke rises. Add the oil and swirl it around. Add the ginger, then the white scallions, and let sizzle for a few seconds to release their aroma. Add the cabbage and, sliding the wok scoop to the bottom of the wok, flip and turn for 3-5 minutes. Then reduce the heat, cover the wok with the lid, and cook for 3-5 more minutes, until tender but