Peel and very finely chop the ginger and deseed and finely slice the chilli (deseed if you like). Toast the sesame seeds in a dry frying pan until lightly golden, then remove to a bowl.
Mix the prawns with the five-spice and ginger, finely grate in the lime zest and add a splash of sesame oil. Toss to coat, then leave to marinate.
Trim the lettuces, discarding any tatty outer leaves, then click the leaves apart. Pick out 12 nice-looking inner leaves (save the remaining lettuce for another recipe).
Cook the noodles according to the packet instructions, then drain and toss in a little sesame oil. Leave to cool, then squeeze over the lime juice.
Scatter over the chilli and sesame seeds, then pick over the coriander leaves. Mix well.
Stir-fry the marinated prawns in a hot wok or frying pan over a high heat for 2 to 3 minutes, or until just cooked.
Pile pinches of noodle salad onto the lettuce leaves, and top each with a couple of prawns, then tuck in.