Step 1

Combine sugar and fish sauce in a small pan; stir over low heat until sugar is dissolved. Cool for 5 minutes.

Step 2

Pour the sugar mixture over the combined mango, lime juice, shallot, chilli and kaffir lime in a large bowl; toss gently until combined.

Step 3

Score fish lightly through the skin twice. Brush fish with the oil; barbecue on a flat plate (or pan-fry) until browned on both sides and just cooked through.

Step 4

Serve the fish with the relish, coriander leaves and extra lime wedges, if desired.