Just coming into season, mackerel is an oily fish, rich in saturated fat, cholesterol and omega-3 fatty acids, and a good source of selenium, and vitamin B12.
As with all fish, seek out a fresh catch - the fish should not smell of fish, should have bright eyes and a firm texture. Mackerel should not droop when held by the head.
Take the fish whole, gut it by slitting the belly where you feel the underside go soft through to the tail. Remove the guts and wash out the cavity.
You could simply slash the skin on both sides, stuff the cavity with lemon, some herbs and place on the grill or under the grill/broiler turning over after a few minutes. The flesh will draw away from the bones with great ease using a fork.
Or, fillet them ...
To fillet, lay the fish flat on a board. With a sharp knife, cut towards the head just behind the little fin on the side. Turn the knife so that the blade is now pointing towards the tail and slide it through the flesh using the rib cage as a natural level. That's your fillet.
Now, feel the fillet. There are still bones in the middle section. You could painstakingly pick them all out with tweezers, which will leave your fillet looking like the cat has already had a go at it! Or, you could slice that little ridge of bones out in a V shape which will leave the fillet with two visible sides.
Pop them on the grill or under the grill/broiler for literally a couple of minutes until the surface can be seen to be bubbling. The remainder of the carcass can also be cooked in the same manner - I usually just remove the head and place the skeleton in alongside the fillets, picking off the last pieces of meat for myself, or not bothering and just letting the cats at it.
Once cooked, they can be cooled and eaten the following day with a salad, whole or shredded, or eaten straight from the grill hot.
Grind some black pepper over and serve with something zingy, tangy, astringent or bitter - my neighbour gave me a bag of peppers that he'd grown, so simply shredded, fillets over and a wedge of lemon does it all for me!