Garlic sauce, known as mojo de ajo, is a favorite topping for Mexican seafood. This version adds a touch of ancho chili. Make the sauce quickly while the fish finishes cooking, and take care not to brown the garlic or chilies. Serve with red or white rice.
Preheat oven to 350 degrees.
Sprinkle fish fillets with salt and pepper. Place a large cast-iron or other heavy-bottomed frying pan over medium-high heat. When hot, add 3 tablespoons of the olive oil. When the oil is hot, add the fish fillets and sear, turning once, until lightly golden on both sides, 1-2 minutes per side. Transfer the fillets to an ovenproof platter or shallow baking dish and place in the oven to finish cooking until opaque throughout, 3-5 minutes depending upon thickness of fillets.
Meanwhile, add the remaining 5 tablespoons olive oil to the same pan and place over medium-low heat. Add garlic, 1 teaspoon salt, and 1/2 teaspoon black pepper. Saute for 1-2 minutes. Add the ancho chili and continue to saute until fragrant, 1-2 minutes longer. Add the fish stock or clam juice and any juices that have collected in the platter or dish holding the fish fillets and raise the heat to medium-high. Boil until reduced by half, 1-2 minutes. Add the lime juice and parsley and bring to a boil, then remove from heat.
Pour the sauce over the fish fillets on the platter. Or, if using a baking dish, transfer the fillets to a warmed platter and pour the sauce over the top. Serve immediately.