Preheat the oven to 220ºC. Brush the sesame oil over the lamb. Sprinkle with five spice powder and rub in evenly.
Place the lamb on a rack in a roasting dish. Roast for 15 minutes for rare, 25 minutes for medium, or 30 minutes for well done. For ease and accuracy use a meat thermometer.
Remove lamb, cover loosely, rest lamb for 10 minutes before serving. While lamb is resting toss together the cooked egg noodles with the carrot, shallots and cucumber. Whisk together the lime juice, soy sauce and caster sugar. Toss with the noodle mixture and coriander.
To serve thinly slice the lamb and serve with the noodle salad and sprinkle with sesame seeds and chilli.
Always rest your meat after cooking. This gives the juices in the meat a chance to redistribute, giving a more juicy and tender result. Transfer the roast to a plate and loosely cover with foil, stand the meat to rest in a warm place.