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 lettuce and, sliding the wok scoop to the bottom of the wok, flip and turn for 2-3 minutes. Then add the salt and oyster sauce. Add the green scallions, stir, and remove to a serving plate.