Bring a large dry frying pan or wok to a mediumhigh heat. Add the cashews and cook for 2-3 mins, tossing occasionally, till golden and toasted on all sides. Tip into a bowl and crush slightly with the end of a rolling pin or a jam jar. Set aside till later.
Roughly shred the Brussels sprouts and pop in a large bowl. Scrub the carrots and slice thinly on the diagonal. Peel and thinly slice the onion. Add the carrots and onion to the sprouts and set aside.
Peel and crush or finely grate the garlic. Peel and finely grate or chop the ginger. Halve the chilli, scraping out any seeds or membrane for less heat. Finely chop the chilli. Separate the coriander stalks and leaves (save the leaves for later), and finely chop the stalks. Toss 1 tsp Szechuan peppercorns into a bowl, and crush with the end of a rolling pin or jam jar. Now you’re prepped and ready to start cooking.
Slice the beef stir-fry strips into bite-size pieces. Pour 1 tbsp oil into the empty frying pan or wok and return to a high heat. When smoking hot, add the beef and sprinkle in a little salt and pepper. Stir fry for 2-3 mins, stirring frequently, till golden brown on all sides. Transfer to a side plate.
Slide the chopped onion, carrots and sprouts into the empty pan. Stir fry for 5 mins, stirring occasionally, till golden and still with a little bite.
Meanwhile, fill a pan with boiling water and add a good pinch of salt. Return to the boil and add the noodles. Simmer for 3 mins, then drain. Rinse well with cold water till cool, then shake dry.
Add the garlic, ginger, chilli, coriander stalks and crushed Szechuan peppercorns to the veg and stir well. Toss in the noodles and stir to combine. Pour in 2 tbsp tamari and the juice from half the lime. Return the beef and its resting juices to the pan. Cook for a further 2 mins to warm through.
Pile the stir-fry onto plates and serve topped with the toasted cashew nuts and reserved coriander leaves, with wedges of the remaining lime half on the side for squeezing.