Clean the fish and remove the entrails. Remove the head, tail, fins and bones. Rinse well with cold water. Boil a liter of water and cool.
Cut the prepared fish into medium-sized slices, no more than 2 cm. Place in a tray, alternately sprinkling with onions, peppers and chopped bay leaves.
Add salt, sugar and sunflower oil to 750 ml of cold boiled water. Stir well until the crystals are completely dissolved. Pour the resulting marinade over the fish so that it is completely covered. Cover the tray with a lid and place in the refrigerator for 12 hours.
Serve the marinated mackerel chilled as a cold appetizer or as a hot side dish. When serving in portions, place on a plate, garnish with a sprig of fresh herbs and olives.