Skin mushrooms and cut off a little bit of the stems
Preheat oven 400 F
Make aluminum foil rings just by shaping aluminum foil into donut shape
Fill mushroom with filling and place them on aluminum rings
Bake until mushroom soften, for 15-20 minutes
Meanwhile, make caramelized onion (of an onion and vegan margarine, fry on medium heat)
Serve immediately and top with caramelized onion