Wipe out the cavity of the fish and slosh in the white wine. Add the lemon, lemon juice, basil, onion and tomato and season with salt and pepper. Preheat oven to 180 degrees C.
Wrap the fish in foil, leaving the head and tail exposed. Brush the exposed parts with oil. Bake for up to one hour, turning every 15 minutes, and checking at 45 minutes to see if it is done.