Mediterranean seafood gratin

3 tbsp olive oil

1 large onion, thinly sliced

1 fennel bulb, trimmed and thinly sliced

3 large garlic cloves, finely sliced

1 heaped tsp coriander seeds, lightly crushed

150ml white wine or vegetable stock

2 x 400g tins chopped tomatoes with herbs

2 tbsp tomato purée

1 bay leaf

1 tbsp fresh lemon juice

1 small bunch flat-leaf parsley, leaves roughly chopped

900g mixed skinless fish fillets, (anything preferred, cut into chunks)

350g raw peeled king prawns

75g finely grated Parmesan

50g panko or coarse dried breadcrumbs

Green salad, to serve (optional)