I have talked with Impossible Burger marketing reps here at our Ithaca Wegmans store about the Burger King grilling procedure and how this impacts the Impossible patty grilling at all Burger kings. To wit: While the burger itself contains no meat, Burger King acknowledges that the Impossible patties are flame-grilled on the same broiler as the chicken and beef products. This means the meatless burger will likely come into contact with bits of meat and poultry as it cooks. What many vegetarians and vegans prefer is the flame broiling taste of this non meat analog. Right now the chief consumer of this Vegetarian non animal meat alternative is the Carnivore/omnivore looking for a lower fat protein alternative that tastes like its animal meat counterpart. 

Clearly the expense of a dedicated flame broiler grilling surface exclusively for Impossible burgers would constitute an exorbitant outlay for Burger King yet the Impossible Burger reps I spoke with at Wegman’s assured me Impossible had placed a clause in the contract with Burger King asking them to provide an alternative grilling/heating procedure for those wishing to have, as advertised, a vegetarian alternative.
Please let me know what a vegetarian should do before ordering an impossible burger at Burger King. The web is replete to references to this Burger King vegetarian dilemma. What I have been told by reps at Burger King is that a microwave option is available upon request by anyone for any reason.   A clear Joint statement from Impossible and Burger King might move things into the light of clarity.

https://www.today.com/food/new-burger-king-impossible-whopper-isn-t-vegetarian-t160203