Put the noodles in a large heatproof bowl and cover with boiling water. Leave to stand for 3 mins or according to pack instructions. Drain in a large sieve, rinse with cold water, then drain well. Tip the noodles into a large salad bowl or deep platter and add the carrot. In a small bowl or jug, mix together the lime juice and the fish sauce. Stir in the chilli and herbs, pour half of the dressing over the noodles and carrot, then toss together. Pile the mango and prawns on top, drizzle with the remaining dressing, then scatter over the crushed peanuts to serve.
An idea: Add in pineapple chunks, apple slices or chilled citrus.