Add half a teaspoon of lime zest to a bowl then flake in the crabmeat. Add the kiwi, shallot and cucumber then squeeze over the juice from the lime and toss to coat the ingredients. Taste and season with salt.
Toast the bread and cut into triangles. Spread with the butter and arrange on a plate next to a bowl of the crab tartare.
For an especially pretty starter, use an 8cm/3in biscuit cutter to cut out four circles from the toast. Spread with the butter then place the biscuit cutter on top and fill with the crab tartare to create neat mounds.