First start the fire and place lava rocks on the fire (or start your outdoor grill). Let the rocks get hot while you prepare the fish.
To prepare the fish, half a passion fruit into the belly of the fish. Then squeeze half a lemon on the inside, and outside of the fish. Sprinkle the salt on the outside and inside of the fish to your liking. Wrap each fish in the ti leaves.
To prepare the imu, lay 2 wet sheets of burlap on the rocks. This creates the steam in which the fish is cooked. Lay ti leaves on top of the burlap to create a bed for the fish wraps. Lay the wrapped fish on the ti leaves and cover with a layer of thick plastic. Then cover the plastic with sand to trap the steam in. If your are using an outdoor grill, wrap the fish in aluminum foil to make a packet. Place fish on outdoor grill and pull down lid to cover.
The fish should be cooked in 15 to 20 minutes depending on the size and temperature of the makeshift oven or your outdoor grill. To uncover, push away sand and pull back the plastic sheet, be careful of rising steam that will rise. Then pull out the wrapped fish, open and serve.