To do this over a wood or coal fire, you will need 2 pounds charcoal or wood. Light the fire and let burn until white ash forms on the coals and flames subside. The fish should be cooked over a gentle fire.
Prepare the fish: Combine soy sauce, olive oil, lime juice, chiles, oregano and black peppercorns. Place the fish in a shallow baking dish and pour the marinade over the fish and let stand for 30 minutes.
Cook the fish over a low fire and baste with marinade. Continue basting until fish is cooked. Skin must be crisp and the flesh should be moist and flaky.
Meanwhile, prepare the sauce: Bring the water to a boil in a medium saucepan. Add the tomatoes, chiles, garlic and onion and cook uncovered for 20 minutes. Cool and puree the sauce in a blender or a food processor. Season with salt.
To serve, transfer the fish to a large platter and cover with the tomato sauce. Garnish the edges of the platter with the cucumber and onion slices and serve with freshly made corn tortillas.
NOTE: The fish could also be broiled in the oven, just do it more slowly than you would a steak or other meat.Makes 4 Source: