To make the dressing, mix all the ingredients together and whisk to emulsify.
Peel and devein the prawns. If they are small, leave them whole. If they are larger, cut them in half lengthways.
Cut each scallop horizontally into about 5 slices. Arrange the slices of scallop on plates with the prawns, drizzle over the dressing, and finish with the coriander and cress.