How to Make It
Preheat the oven to 450°. In a large, enameled cast-iron casserole, heat the 1/4 cup of olive oil. Add the onion and garlic, cover partially and cook over low heat, stirring occasionally, until softened, about 8 minutes. Add the parsley and crushed red pepper and cook over moderate heat, stirring, for 1 minute. Add the tomatoes and cook until almost all of the liquid has evaporated, about 5 minutes. Add the orange zest, season with salt and black pepper and remove from the heat.
Arrange the halibut fillets in the casserole and season with salt and pepper. Scatter the olives over the fish and top with the shrimp and calamari. Season lightly with salt and pepper. Tuck in the clams and mussels, hinge sides down.
In a medium saucepan, bring the clam juice and white wine to a boil. Pour the hot liquid over the seafood. Cover and bake for about 30 minutes, or until the mussels and clams open, the shrimp are pink, the calamari is opaque and the halibut is cooked through. Transfer any unopened clams and mussels to the saucepan and add 1 cup of the cooking liquid from the casserole. Cover and simmer until they open, about 3 minutes; discard any that don't open.
Spoon the seafood and broth into bowls and serve right away, passing grilled bread and additional olive oil at the table.