Heat the oil in a large frying pan or wok and stir-fry the broccoli and carrot for 3 minutes over a medium-hot heat, until the vegetables begin to soften slightly.
Add the spring onions and cook for a further 2 minutes until they are slightly coloured, then stir in the mushrooms. Stir-fry for 3–4 minutes until the mushrooms are just tender.
Meanwhile, cook the noodles in a pan of boiling water for 3–4 minutes or according to the packet instructions until just tender, then drain.
Remove the stir-fried vegetables from the heat, pour in the sweet chilli and soy sauce, then add the noodles and toss to coat. Heap into 2 warmed bowls and serve immediately with extra soy sauce, if desired.