Skin the salmon, remove the line of small bones that run down the middle of the fillet using a pair of pliers, and cut into 3 mm/⅛ inch dice, discarding any grey meat (it doesn’t taste very good and it also looks unappetizing).
Peel the cucumber, discard the centre core of seeds, and dice finely. Ideally, this should be cut into smaller dice than the salmon. Peel one lime and cut the zest into short, fine strips and blanch in boiling water for about 3 seconds – this will greatly enhance its colour. Set to one side. Now squeeze the juice from both the limes. To make the dressing, add one third of the juice to the cucumber, season, and mix in the yoghurt and the dill.
Add the remaining juice to the salmon, season to taste, and mix in well.