Soak chiles in 1 tablespoon vinegar for 10 minutes. Drain. In food process chiles, garlic and cumin to a paste. Add remaining vinegar and process to a thin paste. Rinse fish and pat dry. Place in shallow dish and rub chile paste on both sides. Cover and marinate for 20 minutes. Heat oil in skillet. Add onions and cook for 2 minutes. Reduce heat to low. Add 2 tablespoons water. Cook until onions are golden brown about 10 minutes. Add fish and cook on both sides about 2 minutes per side. Remove from pan and serve.