In a large casserole, heat 3 tablespoons olive oil until hot. Add onions, carrots, and celery. Sweat for 5 minutes. Add the garlic and cook for another 5 minutes. Add Sicilian dried herbs, red pepper flakes, and fresh thyme.
Add the white wine and let it reduce for 5 minutes. Add the clam juice, tomatoes, tomato paste, and fish stock. Stir until well combined and simmer for 20 minutes. Add salt and freshly ground black pepper, to taste.
Add all the seafood, cover, and cook the until just tender, and mussels have opened, about 5-7 minutes.
Garnish with chopped fresh parsley and serve with toasted focaccia bread to dip into the broth.