To make the dressing, combine the water, sugar, fish sauce, vinegar and lemon juice. Stir until the sugar is dissolved. Leave to cool to room temperature.
Cook the vermicelli in a saucepan of boiling water until it is tender but with a bite. Rinse well in cool water, then drain.
Slice the squid tentacles into bite-sized pieces. Slice the tube on 1 side only, then open it up with the inner side facing up. Taking care not to pierce all the way through, score a lattice pattern 4 mm apart over the entire surface.
Cut in half lengthways , then cut into 5 cm squares. Drop the squid pieces into a saucepan of boiling water, then, as soon as they curl up, remove and immediately drop into a bowl of iced water. Drain well, then pat dry with paper towel.
Place the vermicelli, squid, lettuce, carrot, chilli, onion, cucumber, radish and coriander in a bowl. Tear in the mint. Add the garlic and chilli to the dressing and stir to mix, then add the dressing to the salad and mix well. Garnish with the peanuts and fried shallots, then serve.
