First make the dressing, place the lime juice and sugar in a screw-topped jar and shake until the sugar has dissolved. Add the soy sauce, fish sauce, oil and sesame seeds and shake again until thickened and emulsified. Set aside until needed.
Light toast the potato farls in a toaster or under the grill, then carefully cut each one in half horizontally so that you end up with 4 very thin farls. Stack the slices on top of each other and finely slice into “noodles”.
Heat a large non-stick frying pan over a high heat. Add the vegetable oil and then tip in the potato bread “noodles”. Stir-fry for 2-3 minutes until lightly golden and just beginning to crisp up.
Meanwhile, divide the lettuce among serving plates and scatter the mint and coriander leaves on top with the chilli, spring onion and radishes. Add the smoked salmon and prawns and drizzle over enough of the dressing to lightly coat. Pile the warm potato farl “noodles into the middle of each salad and add another light sprinkling of the sesame seeds to garnish.