Cut the head and fins of the fish, then using a sharp knife, score slashes on both sides.
Mix the turmeric and lime juice together in a bowl and season with salt. Arrange the fish in a large dish and rub the turmeric and lime mixture evenly all over the fish. Cover and allow to marinate in the refrigerator for 15 minutes.
Soften the banana leaves, then cut them into 8 x 25-cm / 10-inch squares. Alternatively, use foil squares.
To make the spice paste, put the onion, chilies, garlic, ginger, and desiccated coconut into a blender or food processor and process, adding a little water to make a smooth paste.
Cut the fish into 4 individual portions and coat thickly on both sides with the spice paste.
Spread out the banana leaf or foil squares on a clean flat surface, place a fish portion in the center, then fold over to make a neat parcel and secure with kitchen string (twine).
Heat a thin film of oil on a Tawa, griddle, or a frying pan (skillet) over low-medium heat.
Pan-fry the parcels for 10 minutes on each side. Remove and unwrap carefully so as not to break the fish fillets.