Remove any bones from the red mullet fillets and cut the squid into rings. Clean the shrimp tails and devein.
Chop the onion finely, soften it with the garlic clove in a little oil in a flameproof casserole dish.
Add a little chili pepper, a handful of chopped parsley and the squid. Brown gently, add the white wine and let it evaporate, then add the cherry tomato sauce and about 3 fl oz of water or vegetable broth.
Cover and cook for 10 minutes. Add the shrimp and red mullet fillets and cook for another 5 minutes.
Chop the celery into small pieces, dice the zucchini and pepper, then boil them in salted boiling water for 3-4 minutes.
Add the vegetables to the soup and cook together for another few minutes. Sprinkle with fresh parsley to taste, drizzle with extra-virgin olive oil and serve with slice of toasted bread.