Grind together coconut, basil leaves, curry leaves, green chillies, garlic cloves, sugar, juice of ½ lemon and cumin seeds. Transfer the paste into a bowl, add salt and mix well.
Slit the pomfrets to make pockets. Rub the remaining lemon juice and salt on the pomfrets and stuff the coconut mixture into the pockets.
Roast banana leaves over direct flame.
Grease the leaves with a little oil. Wrap the pomfrets in the banana leaves.
Heat oil in a non-stick grill pan. Place the fish packets in the pan. Cook for 5-6 minutes and flip. Cook on the other side for 6-8 minutes.
Transfer onto a serving plate, unwrap and serve hot.