Wash the mackerels well and remove the heads, smear well with the oil mixed with the black pepper and bake on the grill for 5 min. per side.
Then arrange them in a tray.
Grind the tomatoes and put them to boil until nearly all the water from them evaporates, season with black pepper and salt and add the finely chopped garlic.
Pour the tomato sauce over the mackerels and bake for 15 min. in the oven.