Place the potatoes into a saucepan of cold water, boil until tender then drain in a colander and allow to steam dry.
Season and grill the salmon portions until just cooked. Allow to cool then gently break apart to form large flakes.
Place the cooled potatoes into a bowl and gently mix in the herbs, lemon juice and zest, mustard and seasoning. Fold in the flaked salmon and form into fish cakes.
Lightly dust the fish cakes with the flour, dip into the beaten egg and coat well with the breadcrumbs.
Heat the oil in a saucepan and grill the fish cakes for 4 minutes on each side or until golden brown. Present with the rocket, radish, capers and lime.