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 celery and, sliding the wok scoop to the bottom of the wok, flip and turn for 1-1½ minutes. Then add the salt and green scallions, stir, and remove to a serving plate. Serve immediately.