Put the meat into a dish and pour over 3 tbsp fish sauce. Leave to marinate for 10 minutes.
Cook the noodles according to packet instructions. Drain well, refresh under cold running water ans set aside.
Heat the oil in a large wok until smoking. Stir fry the steak for 3 minutes then add the garlic, spring onions, chillis, green beans and celery. Cook over a high heat for about 2 minutes, stirring all the time.
Add the remaining fish sauce, soy sauce, sugar and lime juice then stir in the rice noodles, mix well and fry for a further 1-2 minutes.
Serve garnished with coriander and mint leaves.