Seafood stew so make the stew base first and add the fish at the last minute

2 tbsp olive oil, plus extra for drizzling 1 onion, finely chopped 2 celery stalks, finely chopped salt and freshly ground black pepper 1 tbsp dried oregano 1 fennel bulb, trimmed and roughly chopped 1lb (450g) cleaned squid, sliced into 1⁄2in (1cm) rings 11⁄2 cups dry white wine 2 lemons, zest peeled into strips using a vegetable peeler 1 tbsp tomato paste 14oz (400g) can chopped tomatoes 2 cups hot fish stock for the slow cooker (3 cups for the traditional method) 21⁄4lb (1kg) mussels, scrubbed and debearded (discard any that do not close when tapped) 9oz (250g) raw shelled king prawns 12oz (350g) sea bass filet (or other white fish such as haddock), skinned and cut into chunky pieces few sprigs of flat-leaf parsley, finely chopped in the slow cooker PREP 20–30 MINS COOK 15 MINS PRECOOKING; HIGH 3–4 HRS Preheat the slow cooker, if required. Heat the oil in a large heavy-based pan over medium heat, add the on...