Heat the olive oil in a large frying pan and add the seasoned hake fillets, skin side down. Cook for a couple of minutes until the skin is just beginning to crisp, then add little knobs of butter to the pan around each hake fillet and cook for another couple of minutes until the skin is crisp.
Preheat the oven to 200°C/fan180°C/gas 6. Scatter the fennel, onion and chilli in a roasting tin and drizzle with 1 tbsp olive oil and the lemon juice. Roast for 10 minutes.
Mix the mustard powder with a little lager in the bottom of a small pan to make a paste, then stir in the rest of the lager and add the butter. Heat gently to melt the butter, add the cheese and stir to melt, but do not let the mixture boil. Once smooth, add the chorizo.
Season the brill and prawns with salt and pepper. Heat the rapeseed oil in a large, non-stick frying pan until hot but not smoking, then place the fish fillets in the pan and fry over a medium–high heat for 3 minutes. Turn the fillets over and then add the prawns and butter to the pan.
Pre-heat your oven to 200ºC/400ºF/gas. Season the cod with salt and pepper, place on an oiled baking tray and lay two slices of pancetta over the top of each fillet.
Place the four lemon halves, cut side down, on the tray next to the fish. Roast in the preheated oven for 10–15 minutes.