Heat the olive oil and gently fry the onion until soft and fragrant. Add the ripe tomatoes, tinned tomatoes and tomato purée and simmer for a few minutes.
Stir in the spices and garlic and allow the flavours to infuse. Ladle in the fish stock and some harissa paste and leave to simmer for another minute or so.
Add the leeks, fish, calamari, prawns and shrimp and allow to simmer for 10 – 15 minutes. Add the roasted red pepper and scatter over the herbs and lemon zest over the top and serve with fresh, ripe lemon wedges and chunks of crusty bread.