The rich, fatty, marbled meat from the belly of the tuna fish (toro) is the most sought-after cut. Salmon has similar marbled fat, and some producers of pre-packaged salmon fillets call this «belly loin» on their packet labels. You will probably have trouble finding the Japanese citrus fruit, yuzu, in Norway, but you can use a slightly bitter orange or a sweet lemon or lime instead.
Chop the salmon into cubes and place it in a bowl with the cucumber and spring onions. Wash the yuzu and grate about 1 tbs. of the peel. Cut the citrus fruit in half and scoop out the pulp from one half. Coarsely chop the pulp and mix this and the grated peel with the other ingredients.
Fold in the soy sauce and strain.
You can now serve it in small dishes with a bit of salmon roe on top of each portion.