To make the pickled cucumber, combine all the ingredients in a bowl, cover and refrigerate. Cook the sushi rice according to the packet instructions and keep warm.

To assemble, lay a nori sheet (rough side up) on a piece of clingfilm. With wet fingers to prevent sticking, position a quarter of the cooked rice in the centre of the nori sheet and shape it into a square, ensuring that the flat sides of the square face the corners of the nori sheet. Season with a pinch of salt.

Position half the salmon, avocado, lettuce and a spoonful of the cucumber pickle on top of the rice so that it is roughly square. Put another quarter of the rice on top of the filling, and compact down into a square as before. Season the rice with a small pinch of salt.

To enclose the filling, wet your fingers and fold the corners of the nori sheet into the centre to create a square-shaped, sealed parcel with the filling inside. Gather the clingfilm around the parcel and gently press down to compact.  Set aside for 5 mins for the nori sheet to soften and stick to the rice. Repeat with the second parcel.

To serve, slice a line through the centre of the nori with a wet sharp knife, cutting through the clingfilm and sandwich. Remove the clingfilm and serve immediately.