1. Season the cod with salt and pepper.2. Place the basil, parmesan, walnuts, garlic, grated lemon plus lemon juice and oil in a food processor and process until finely chopped.
3. Spread the marinade over each piece of the fish. Cover and chill for a minimum of 2 hours.
(I always leave them overnight in the fridge).
4. Place fish on to a separate tinfoil squares. Cut the butter into small cubes and place over the fish.
5. Loosely fold the foil over the fillets to enclose the fish and to make a parcel.
6. Cook over medium-high heat for about 10-15 minutes.