1Roughly chop the salmon or trout, and combine it in a bowl with the remaining ingredients. Set a heavy skillet over medium-high heat and add a drizzle of oil. Shape the mixture into four patties and place them gently into the pan; cook until deep golden on one side, then flip and cook on the other side - they should cook through and be crusty and golden in about 5 minutes.
2To make the caper mayo, stir together the mayo, lemon juice, capers and pepper. Spread on the buns and top with salmon patties, tomato, lettuce and thinly sliced cucumber - and a little more caper mayo. Serve immediately.