Look for banana leaves in the frozen section of Asian or Latin supermarkets.
This is insanely fresh and delicious (particularly when the fish is right out of the water). We had this on a boat in Indonesia.
1 lb Spanish mackerel fillet
6 medium shallots, peeled
2 medium garlic cloves, peeled
2 red chilis, seeded
5 candlenuts (tropical nut used often in Indonesian cuisine – Macadamia nuts are a fine substitute)
2 tomatoes (for the spice paste)
1 1/2 tbsps tamarind paste, soaked in warm water
sliced tomato (to top the fish)
kaffir lime leaves
banana leaf, for wrapping
1. Grind ingredients 2-7 into a smooth paste. (We think this works best in a food processor.)
2. Cut fish fillet into desired size (the chef recommends the size being the width of 2-3 fingers). Mix with the spice paste, season with salt, and marinate for at least two hours.
3. Place the fillet in banana leaf and top with tomato slices and lime leaves. Wrap up the fillet with the banana leaf.
4. Cook over a grill or pan with low fire until fish is cooked through (around 5 minutes).