I love rich, oily fish such as mackerel, sardines and anchovies. These types of fish have a lot more flavour than most white-fleshed fish, and I like to serve them with something acidic, which balances the richness. For this grilled mackerel dish, I make a cucumber salad that's seasoned with fish sauce, fresh lime juice and chillies. Butterflying the fish so the flesh is intact, minus the bones and heads is harder to describe than it is to do. If you have a good fishmonger who is willing to do...