Trim the meat of any fat and then cut across the grain evenly into thin slices. Heat 2 tbsp oil in a pan, swirling gently to coat the sides. Stir-fry the lamb in small batches over high heat until browned but not cooked through. Remove from the wok and drain on paper towels.
Heat the remaining oil and stir-fry the onion and snow peas for 2 minutes. Add the bamboo shoots and stir-fry for 1 minute.
Return the meat, add chilli and soy sauce. Stir-fry over high heat until the meat is cooked and the sauce is hot.
Add in the cashew. Season with salt and black pepper to taste. Mix well.