First cook the noodles according to the packet instructions, then drain and set aside.
To make the stir fry sauce, whisk all the ingredients together in a jug and check the seasoning.
Slice the steaks against the grain into finger-sized strips and season with sea salt and black pepper.
Heat the oil in a wok, deep frying pan or non-stick pot until it's almost smoking. Add the seasoned pieces of steak and stir-fry for 1 to 2 minutes.
Throw in the carrot or sweet potato and keep it moving around the pan for 90 seconds. Add the peppers and cook for 2 to 3 minutes, then add the broccoli, pak choi, green beans and sugar snap peas and cook for 1 minute more.
Add the shallot, garlic, chillies, if using, and the ginger and cook for 1 minute, stirring constantly so that nothing sticks. Pour in the sauce, then add the cooked noodles and toss everything together until well combined.
Divide the stir-fry between your serving plates and garnish with the spring onions.