Dice the tomato and cucumber into 5mm cubes. Mince the onion and soak it in water, then drain.

Mix the sauce ingredients (salt, vinegar, black pepper) in a bowl. Add the diced vegetables and mix well. Chill in the refrigerator for 30 minutes.

Cut the Pacific saury in half and season both sides with 1/2 tsp salt. Pat dry with paper towels.

Heat a frying pan with olive oil spread thinly using a paper towel over medium-low heat. Cook the saury for 5 minutes on each side until golden and cooked through.