It seems that in some places they already have one, in germany we have the Veggie-Burger TS https://www.mcdonalds.de/de/produkte/produkt-profil?productName=vegg

It seems that in some places they already have one, in germany we have the Veggie-Burger TS https://www.mcdonalds.de/de/produkte/produkt-profil?productName=veggieburger_ts https://www.mcdonalds.de/de/produkte/produkt-profil?productN.... I liked it when I tried.