Place the capers in a bowl with the olive oil and the lemon juice and zest. Add a spoonful of the minced herbs and stir to combine. Cut the tomatoes in half horizontally. Heat a grill pan and grill the tomatoes for 3 minutes on each side. Transfer to serving plates and lightly salt each half. Place 1 mackerel fillet on each tomato half and top with the caper mixture and remaining herbs. Decorate with more rinsed capers.

Capers are the flower buds of the caper plant. They are picked before they open and can be preserved in salt or vinegar. Capers are used to flavor dishes and pair well with a wide variety of foods, from meat to fish to pasta. The fruit from the caper plant, called caper berries, has a similar but more delicate flavor.