Place a piece of aluminium foil large enough to wrap the fish fillet
in on bench and using about a tablespoon of olive oil, grease the
foil. For extra security, double the foil on the bottom where it will
be sitting on the barbecue. Place the fish on the oiled foil, put the
tomato, onion and basil on top, sprinkle with salt and pepper if you
wish. Fold the foil over, making sure that it is completely sealed.
Place the foil parcel on the grill section of the barbecue once the
flames have died down and it is only coals. Cook for approximately 15
minutes (depends on the thickness of the fillet). This is also lovely
with a little bit of sweet chilli sauce poured over the tomato and
onion before you cook it. Serve immediately.