There was an article a while back, that exposed the carcinogenic *glyphosate* in the plant burgers at Burger King; it soon went down the memory hole.
https://www.momsacrossamerica.com/gmo_impossible_burger_positive_for_carcinogenic_glyphosate
https://www.nuorigins.com/did-you-know-there-is-cancer-in-your-impossible-burger/
Burger King’s flame broiling is said to be carcinogenic itself, so they were just trying to lend their veggie product more authenticity. Most thoughtful of them.