Preheat the oven to 160°C (140° fan-forced). Line a large baking tray with baking paper.
Heat oil in a medium heavy based saucepan or wok (oil should come about halfway up the side over medium-high heat (180°C).
In a shallow dish combine flour, pepper and salt. In a separate shallow dish place egg whites. Dip lamb in egg, and lightly coat in flour mixture, shaking off any excess. Fry lamb in batches for 2 to 3 minutes or until lightly golden. Transfer lamb with a slotted spoon to prepared baking tray and place in oven to keep warm while cooking remaining lamb.
Prepare noodles according to packet instructions. Rinse under cold water, drain and cut into 10cm lengths.
In a large bowl place carrot, cucumber and radishes. Add the vinegar and sugar and toss well to combine. Set aside for 5 minutes to pickle. Add noodles, mint and coriander and toss to combine
Serve lamb with noodle salad, Vietnamese dipping sauce, lime wedges and chilli flakes, if desired.