Cut the salmon slices into 3 x 5 cm (1¼ x 2 inch) rectangles. Remove the stone from the avocado half, cut in two and remove the skin. Then cut each quarter into four or five slices lengthways and cut the slices in half through the middle. Place the pieces in a bowl and toss in the lemon juice.
Roll a piece of avocado or a prawn in each piece of salmon and place