For the coconut miti
To make the coconut miti, combine all the ingredients except the coriander stems in a medium-sized bowl. Set aside.
Build a medium-hot fire in a charcoal grill, or heat a gas grill to high.
Lay the banana leaves on a clean work surface, overlapping them to form a piece large enough to wrap and enclose the whole fish.
Place the fish in the centre of the banana leaves and prepare it by cutting a slash lengthways down to the bone, then crosswise in 2 places, spacing apart; repeat on the other side.
Season the fish cavity and skin with salt and drizzle with oil.
Stuff with lime slices and herb stems and season well.
Wrap the banana leaves to enclose the fish then place on the barbecue and cook, turning once, until just cooked through (7-8 minutes on each side). Open the parcel and serve the fish with the coconut miti sauce and lime wedges.