Cut the fish into cubes. Clean and wash spring onion and cut into fine rings. Wash cucumber, cut off 8 thin slices. Cut the rest into fine cubes. Wash coriander, shake dry and chop leaves, except for something to garnish, from the stems.
Mix soy sauce, wasabi, coriander and lime juice. Mix salmon, spring onion and cucumber and marinate with the sauce. Spread on the bread slices and garnish with halved cucumber slices and coriander.