Mullet with Lime

• 3 lb (1.4 kg) red mullet fillets
• 1 small onion, finely chopped

Pre-heat the oven to gas mark 4, 350°F (180°C). Place each fish fillet on a square of aluminium foil. Mix together the other ingredients and pour over the fish. Bring up the edges of each foil square and seal to make a parcel.