Clean the horse mackerels and flake the fillets, removing any bones thoroughly to make sure there are no bones left. 
Meanwhile squeeze a grapefruit and add the juice in a deep plate with coarse salt and a tablespoon of sugar. Steep the fish in brine for ten or twelve minutes.
Wash, peel the mango and slice it into thin slices (maximum thirty millimetres width) trying to give the same shape.
With the rest of the fruit, make some strips of mango to decorate the dish and add the left of the fruit with the olive oil, the milk, a pinch of pepper and salt into a food processor and blend roughly until a creamy sauce forms.
Preheat the griddle and place the sliced mango until lightly roasted. Set aside.
Take the fish from the brine and cook it all in the griddle for over twenty or thirty seconds until golden brown.
To plate the dish, pour the mango sauce into the plate. Then, place the some slices of mango over it and a fillet of horse mackerel. Repeat the same process with the remaining slices and fillets. Add some more sauce and serve with some vegetable salad and the strips of mango.