Steam or boil the cabbage for 3-4 mins until just tender, then drain well. If doing ahead of time, cool under running water and chill until ready to stir-fry.
Heat the oil in a wok or large frying pan. Add the garlic and seeds and cook for 1 min until beginning to turn golden. Toss in the cabbage and stir-fry over the highest heat for 3-4 mins. Season with a little sea salt and serve.