At the Playa Principal in Puerto Escondido, fishermen bring whole fish to the cooks on the beach who clean and cook them. To prepare a whole fish for cooking it a la talla in their style, scale it, cut off the fins (I find a kitchen shears works good for that) but don’t gut it. Then, use a sharp knife to cut along one side of the dorsal fin (the one on top of the fish as it swims), from the back of the head to the tail, cutting into the fish along the spine until you reach the backbone. Use your knife to cut through the rib bones that surround the viscera. Flip the fish over and do the same on the other side. Now the two fillets should be separated from the spines and back bone, but still connected at the head and tail. Holding the backbone firmly, break it (or cut it) from the head and from the tail; discard or save for stock. With a cleaver or heavy knife, split the head without cutting all the way through it. Pull out and discard all the viscera, then rinse the fish well. You now have a completely butterflied whole fish (butterflied from the top down, not the bottom up), with only the lower rib bones attached. Feel free to cut them out.
From Season 9 - Mexico: One Plate at a Time
Making the marinade. Roast the garlic in an dry skillet over medium heat until soft and blotchy black in places, 10 to 15 minutes; cool until handleable, then peel of the papery skin. A few at a time, toast the dried chiles, using a metal spatula to press them against the surface of the hot skillet for a few seconds until they release their aroma and change color slightly. Collect the toasted chiles in bowl, cover with hot tap water, weight with a plate to keep them submerged and let rehydrate for about 30 minutes. Drain, reserving ½ cup of the soaking liquid.
Place the chiles in a blender or food processor along with the reserved soaking liquid, the garlic, oregano and black pepper. (If you’re using a blender and the mixture just won’t move through the blades, add more water, a little at a time, until everything is moving, but still as thick as possible.) Press through a medium-mesh strainer into a bowl to remove unblended skins and stray seeds. Taste (it’ll have a rough, raw edge to it) and season with salt, usually a scant teaspoon.
Grilling and serving the fish. About 20 minutes before cooking, prepare a charcoal fire, letting the coals burn until they are covered with a gray ash and are medium hot.
Brush or spray oil on both sides of a hinged grill basket (I like the one that has flexible wires that will mold around the fish). Spray or brush oil on both sides of the fish fillets (or butterflied whole fish), then sprinkle with salt. Lay the fish on one side of the basket and close it. Lay the basket over the hot coals with fish skin-side up. Cook until the fish begins to brown, 4 or 5 minutes (it’ll probably be a little longer for the whole fish), depending on the heat of your fire. Flip the basket, carefully open it up, freeing any sticky bits of fish, then slather the top generously with the marinade. Dot with dollops of the mayonnaise mixture and cook (you can leave the basket open) until the skin crisps and the marinade becomes glossy, another 5 minutes or so. Remove the basket from the fire.
Carefully free the fish from the bottom part of the grill basket and transfer it to a platter. Garnish with lime wedges and serve right away.