Heat the olive oil in a 7-to-8-quart enameled cast-iron Dutch oven over medium-high heat. Season the fish with salt, then cook until browned, about 2 minutes per side. Transfer to a plate. Add the onion, garlic, fennel, chile pepper and carrot to the pot; reduce the heat to medium and sweat the vegetables, about 2 minutes. Add the chorizo and cook until browned, about 2 more minutes. Add the sherry and bring to a simmer, scraping up any browned bits from the bottom of the pot with a wooden spoon.

Crush the tomatoes with your hands and add to the pot with their juices. Add the saffron, chicken stock and clams and bring to a simmer. Cover and cook until the clams just begin to open, about 3 minutes. Add the swordfish to the pot and simmer, covered, until the swordfish is cooked through and the clams open, about 7 more minutes. (Discard any clams that do not open.) Stir in the olives, parsley and basil. Serve with grilled bread.