Step 1: Make the spice paste: Place the macadamia nuts, ginger, shallots, garlic, chiles, turmeric, and black pepper in a food processor and grind to a fine paste, running the machine in short bursts. (You can also pound the ingredients to a paste in a heavy mortar with a pestle.) Work in fish sauce or soy sauce.

Step 2: Heat the oil in a skillet over medium-high heat. Add the shrimp paste (if using) and fry for 1 minute. Increase the heat to high, add the spice paste, and fry it until dark and fragrant, 4 to 6 minutes, stirring with a wooden spoon. Transfer the spice paste to a plate or bowl and let cool to room temperature. Using a spoon or spatula, thickly spread each piece of fish on both sides with spice paste.

Step 3: Lay a banana leaf square, dark side down, on your work surface. Place a piece of fish in the center. Fold over one side, then the other, to encase the fish. Then pin each end with a toothpick to seal the package. Each package will be about 6 inches by 4 inches. The fish packages can be prepared several hours ahead and refrigerated until grilling.

Step 4: Set up your grill for direct grilling and preheat to high.

Step 5: Arrange the banana leaf packages, smooth side down, and grill until nicely browned, 4 to 5 minutes. Turn the packages over and grill the same way-total cooking time should be 8 to 10 minutes. To test for doneness, insert a metal skewer through the side of one packet and leave it for 15 seconds: it should come out very hot to the touch.

Serve the fish in the banana leaf. Let each eater open his own package.