Bring a pan of salted water to a boil. Add the noodles and cook for 2-3 minutes, until just tender. Drain and toss with 2 tablespoons of the oil. Heat the remaining oil in a wok or frying pan until very hot. Add the onion, ginger and garlic and stir-fry for 2-3 minutes. Add the asparagus and stir-fry for 2-3 minutes more. Add the egg noodles and bean sprouts and stir-fry for 2 minutes. Stir in the scallions and soy sauce. Season with salt and pepper, adding salt sparingly, as the soy sauce will probably supply enough salt in itself. Stir-fry for 1 minute, then serve at once.