Barbecued Kingfish Fillet with Sauce Vierge

Kingfish is considered an oily, medium-flavoured fish, good both raw and cooked, and when it is not overcooked it is moist and has a nice firm texture. It is known as yellow tail in Australia and as hamachi in Japan and America. I have always enjoyed the wild-caught fish in Australia, but in the last couple of years there has been much interest in a new farmed species called hiramasa kingfish. It is available both here (from South Australia) and overseas. It is a large, handsome fish weighi