Burger King doesn't use a grill at all. They flame-broil their burgers. I believe some (or all?) of them use a Nieco ( https://nieco.com/ https://nieco.com/ )

Burger King doesn't use a grill at all. They flame-broil their burgers. I believe some (or all?) of them use a Nieco ( https://nieco.com/ https://nieco.com/ ) brand broiler that basically has a metal conveyor belt that carries the patty through a flame. See this video: https://www.youtube.com/watch?v=GSuLWkBt5MI https://www.youtube.com/watch?v=GSuLWkBt5MI They could, if they wanted, designate one lane solely for Impossible patties (and other non-meat products). If they don't, looks by the time the belt makes it way back through the flame, whatever residue on it will have been mostly reduced to ash. I would guess the belt wouldn't transfer meat grease and crumbs onto a veggie patty as much as a grill would. But, after it leaves the belt, it slides down to a holding area, where it would come into contact with whatever else was on the belt before it.