Put the stock in a large pan, place over a medium-low heat and bring to a gentle simmer. Add the chicken and poach for 15 mins until cooked through with no pink remaining. Remove with a slotted spoon, leaving the stock in the pan. Use two forks to shred the chicken and set aside.
Add the noodles to the pan of stock and simmer for 3-4 mins until just tender. Drain, reserving 300ml of the stock.
Heat the oil in a wok or large frying pan. Add the ginger, garlic, five spice and chilli and stir-fry for 1 minute. Add the mixed pepper stir fry, mange tout and spring onions. Stir-fry briskly for a further 3 mins. Add the shredded chicken, noodles, soy sauce and reserved stock. Heat through for 1 minute, then serve.