Heat wok in oil over high heat, add the ginger and stir fry for 10 seconds, then add the onion. Cook onion for 30 seconds until starting to soften, then add the beef.
When the beef is browned, add the noodles, Sauce and water and stir fry for 30 seconds or so until the sauce has thickened. Toss in the bean sprouts and quickly stir, then remove from heat. Serve immediately.