Just to keep the record straight, Burger King used to serve a very good vegi Burger based partly on mushrooms and walnuts. I ordered them all the time, and they were delicious, especially with cheese. They dropped this wonderful offering when they introduced the Impossible Burger, which was horrendously, even impossibly bad. It’s a shame if they don’t bring back their original vegi burger menu, but I don’t expect it to happen.
I’d do a mushroom and walnut burger. Throw the traditional lettuce, tomato and onions on that you get with the Whopper, that would be a good sandwich