Bread slices or breadbuns can be used.
It is possible to make it gluten free by using gluten free bread.
Mushrooms (I usually use Portobello mushrooms)
Extra virgin olive oil
Vegetable cream (Soya option makes a thicker sauce)
After washing and cutting the mushrooms in quarters or slices, put them in a pan, add some olive oil and salt to taste. Cook on slow heat. When ready add the cream and let it mix for a few minutes. Pour it on toast. You can add some ground pepper on top.