If you put spinach on something, it's "florentine," and if you put mushrooms on a dish, it's "swiss." Those are the rules, I don't make them. (This burger isn't so much of an alternative burger, but I did put it on pita bread. So there's your alternative.)
I sautéed and seasoned the mushrooms in the pan that I cooked the burgers in. I put the 'shrooms on the burgers, melted the swiss on top, and added Country Bob's steak sauce. If you're not familiar with Bob's, you should get there. Like Tracy Morgan says, "I'm down" with Bob's "like four flat tires." If you put Bob's on a bank vault, I think I'd gnaw through the steel door. This sauce would make me eat my mother's pork chops.
I liked the whole-wheat pitas on these, because the bread was basically a vehicle for what was between it: the meat, cheese, mushrooms, and the Bob's. In fact, with those toppings, you could easily use turkey meat or a veggie patty, and it would still taste good. (Not as good, but that's just my opinion).