Place the pork fillet on wire rack over a roasting tin half-filled with water. Roast at 180°C (350°F, gas mark 4) for 30 mins. Remove from the oven and brush with hoisin sauce. Return to oven and roast for 20-25 mins, until cooked and slightly charred in places. Cover the pork and set aside.
Cook the noodles in a large pan of boiling salted water according to packet instructions. Drain well and toss in half the sesame oil.
Heat the rest of the oil in a wok or frying pan. Add the peppers, spring onions, mangetout and baby corn and stir-fry over a high heat for 2-3 mins.
Add the noodles and soy sauce and stir-fry for a further 1-2 mins until heated through.
Thinly slice the roast pork and add to the wok. Toss gently to mix, then serve in warmed bowls.