If your fishmonger hasn’t already done so, clean and prepare your chosen fish and shellfish. Cut fish fillets into large chunks and seafood into manageable pieces.
Put the oil, onion and garlic into a large pan and fry briefly.
Add the tomatoes, wine, chilli, parsley and fennel seeds and season with salt and pepper. Cook for 15 minutes.
Start to add large pieces of fish to the sauce first and those that will take the longest to cook such as monkfish, then add the more tender fish such as red mullet or sole and the shellfish, ending up with the mussels if using. Cook for five or so minutes, or until the fish is cooked and the mussels have opened. (Discard any mussels that haven't opened.)
Rub the bread with garlic, drizzle with olive oil, and put each slice in the bottom of a deep soup bowl. Pour over the soup and serve.