Soak ancho chili in a 1 cup of warm water for 4 to 6 hours.
Preheat broiler to high.
Remove chili from water. In a medium bowl, place chili, bell pepper, tomatoes, and onion and coat with 2 tablespoons olive oil.
Once coated, place on a large baking sheet lined with parchment paper and broil for 10 minutes, until charred.
In a blender or food processor, add 3 tablespoons olive oil, ingredients from baking sheet and the next 6 ingredients (garlic through salt and pepper).
Blend 1 to 2 minutes until combined, but still coarse.
Preheat oven to 400 degrees.
Place fish in a baking dish and coat with remaining olive oil and lemon juice. Add salt and pepper to taste, and bake for 10 to 12 minutes until the fish flakes easily with a fork. Serve with Romesco sauce.