Cook the noodles following pack instructions. Meanwhile, heat half the oil in a wok and stir-fry the beef over a high heat for 30 seconds until browned. Tip onto a plate, set aside, then add the remaining oil to the wok. Stir-fry the onion and ginger until softened. Add a drop of water to prevent burning, if needed and cook covered for 2-3 mins.
Stir in the mushrooms and garlic, and fry until they start to soften (around 3 mins), then add the beansprouts and cook for a minute or two more until piping hot.
Mix the tamari and vinegar together in a small bowl with 2 tbsp water. Add the drained noodles to the wok, toss well, then add the tamari mixture, spring onions and the beef. Stir-fry for a few minutes until heated through. Season with plenty of black pepper and serve.