Trim the sirloin steaks and cut into thin strips. Cover and set aside.
Cook the noodles in a saucepan of boiling water for 4 minutes, or according to the packet instructions. Drain the noodles well and set aside.
While the noodles are cooking, heat a wok or a large heavy-based frying pan until hot. Peel and finely slice the onion and garlic clove and chop the peppers. Add half the oil and swirl to coat the wok, then add the onion and peppers and stir-fry for 3 minutes. Add the five-spice powder and garlic and stir-fry for another minute. Remove and set aside.
Add the remaining oil to the wok, turn up the heat and add the steak strips. Stir-fry for 3 minutes. Return the peppers and onions, then add the mange-tout and stir-fry for a further 2 minutes. Pour in the stock, stir well and bring to the boil.
Add the noodles to the wok, and toss everything together. Heat and stir for 2–3 minutes until all the ingredients are well combined. To finish add the soy sauce, black pepper and coriander leaves. Serve immediately!