Prep the marinade in a large tray.
Gently fry the mushrooms in oil on each side for 5 minutes, then start to slowly press down until golden brown on each side.
Soak the mushrooms in the marinade for 30 minutes - 2 hours.
Prep the pickled onions and mayo (or get store bought).
Fry the marinated mushrooms in oil on a medium - high heat until charred.
Load up the sandwich and enjoy!
