Place beef slices into a small bowl, toss through the cornflour to coat, mix through soy sauce and set aside.
Mix together sauce ingredients in a small bowl.
Bring a large pot of salted water to the boil, add noodles and cook according to packet instructions. Meanwhile, heat a large frypan or wok over high heat, add oil and onion and fry until slightly charred.
Add garlic, ginger and mushrooms, stir fry for 2 minutes and set aside.
Heat remaining oil in the pan, add beef and stir fry until browned.
Return the vegetables to the pan with the noodles, sauce, spring onion and bean sprouts and toss well to combine.
