You can skip this step if you prefer this tapa cold. Heat a non-stick frying pan, add a spoonful of olive oil and very carefully fry the mackerel fillets for one minute on both sides.
Chop the garlic into very fine pieces, sprinkle with salt and make into a spread. Then mix with a spoonful of olive oil and parsley.
Coat the mackerel fillets with a mixture of oil, garlic and parsley.