Place all the ingredients in a small bowl and whisk to combine.
Place the beef strips in a non-metallic dish and pour over the marinade. Cover and leave to marinate for about 10 minutes.
Meanwhile, cook the noodles in boiling water until tender, about 6 minutes. Drain and refresh under cold water. Add a dash of oil and toss to prevent them sticking together.
Heat a wok until hot. Add a good dash of oil, and when hot, add half the beef and stir-fry for 1-2 minutes. Transfer to a plate and repeat with remaining beef. Keep remaining marinade.
Add another dash of oil to the wok. Add the broccoli and beans and stir-fry until partially tender. (Add a dash of water or stock if the vegetables look dry and are colouring too quickly). Add mushrooms, spring onion and chilli. Stir-fry until all vegetables are just tender, about 5 minutes. Return the beef and remaining marinade to the wok, toss quickly then serve immediately.