Slash each mackerel diagonally 3 or 4 times on each side, then place them in a bowl. Mix together the garlic, spices, olive oil and lemon juice, then rub the mixture all over the mackerel. Cover and put in the fridge to marinate for 20 minutes.
Heat a large griddle pan over a medium heat (or even better, heat a barbecue until hot, the flames have died down and the coals glow softly). Ad