Simmer the husks in water to cover for 10 minutes, weighing them with a plate to keep them submerged. Remove from the heat and let stand for a few hours until pliable. Place the toasted anchos in a bowl and cover them with the vinegar and warm water. Soak for about 20 minutes, then pour the mixture into a blender. Add the cumin seeds, oregano, thyme, salt, garlic, and vinegar. Blend to a smooth paste. Cut the fish into 3 by 1 inch batons and place in a ceramic or glass bowl. Add 6 tablespoons of the chile paste and mix together gently but thoroughly. Cover and refrigerate for 1 to 2 hours.
Separate out 18 of the largest and most pliable husks, at least 6 inches across on the wider end and 6 to 7 inches long. If you cant find enough good ones, overlap some of the larger ones to give a wide and strong unbroken surface to spread the dough on. Pat the leaves dry with a towel. Make ties for the tamales by cutting a few of the husks into strips. Divide the marinated fish into 6 equal portions. Spread 1 teaspoon of the reserved chile paste over a 2 by 3 inch area on the wide end of a husk. Lay half of one portion of fish over the paste. Sprinkle with a little salt and top with the remaining half portion of fish. Fold over the sides and then the ends to enclose the filling. Lay the finished package flap side down, repeat the operation to double wrap the fish and tie it twice around its width with the cornhusk strips. Continue to form the other 5 packages in the same way.
About 20 minutes before serving, heat a large griddle or a grill to medium high heat. Grill the packages for about 6 minutes on each side, until the husks have blackened. Open one of the packages to test for doneness, taking care not to let out any of the precious juices. Remove the strings from each package and carefully pull away the outer layers of husk. Set each package on a heated dinner plate and carefully remove the last husk, pushing the fish out onto the plate. Drizzle a little olive oil over the fish and scatter with a little onion and chopped cilantro. Serve the lime wedges on the side. Pass the warm corn tortillas, mashed avocado, diced cucumber, and chiles at the table.
c.1997, M.S. Milliken & S. Feniger, all rights reserved