You will need:
I prepared the butter before I left by crushing three garlic cloves into about 50g butter and mixing it together with a few sprigs of chopped parsley and some black pepper.
Take the mushrooms and wrap them (gill side up) in some foil so they are completely covered. Put the parcel onto the edge of the BBQ, so it is not directly over the heat, and leave them to soften in their own juices for about 20 minutes. When they are soft put a little of the garlic butter onto the mushroom gills and leave the parcel open so that some of the moisture evaporates. After about five minutes toast the buns on the BBQ and put a mushroom in each bun.