Mix all the marinade ingredients together.
Place the mushrooms (stem side up) in a baking pan.
Pour the marinade into the mushroom caps.
Heat your oven to about 200ºC (let the mushrooms sit in the marinade until the oven's hot).
Put the pan in the oven, and leave for about 15-20 minutes. The bigger (and thicker) the mushrooms, the longer they'll need.
Remove from the oven once they're looking soft and juicy.
Serve on a burger bun with vegan mayo, lettuce and tomato, or alongside some veggies and a whole grain.