Thoroughly clean the mackerel and sprinkle it with salt and pepper inside and out. Arrange in a greased tray and sprinkle them with crushed parsley and crushed walnuts.
Mix the oil with the pressed garlic, tomato salsa and a little vinegar. Pour this aromatic sauce evenly over the fish. Put them to bake in a moderate oven until ready, initially this may be done under foil.
Serve 1 baked mackerel with parsley and walnuts with a few slices of lemon per serving.