Using a very sharp knife, cut the tuna into 5mm thick slices.
Arrange the fish on 4 plates, slightly overlapping the slices.
Put the lime juice in a bowl.
Split the finger limes in half lengthways, remove the pearls from the pith and add to the bowl along with the olive oil.
Season with salt, then spoon over the fish.
Give the fish a good grind of black pepper, then sprinkle with the coriander and serve immediately.
