How to barbeque the best mushroom cheeseburger?

To me, the absolute best mushroom cheeseburger has portabello mushrooms. I saute them with garlic, soy sauce and olive oil before topping them over the cheese and usually just go with the mushrooms, mustard and cheese on my bbq'd burger. However, I have...

only had brown mushrooms, white and portabellos on my burgers...the portabellos win, hands down.

It's barbeque season and I'm an amatuer. How would you make the ultimate bbq mushroom cheeseburger?

I'm with you on the portobello - great on a burger.

Here's my version of the mushroom cheeseburger:

-hickory smoked all-beef patty (mix the patty with the liquid smoke, garlic, onions,salt and pepper)
-portobello marinated in balsamic vinegar and grilled until tender
-top the patty with provolone and let melt
-on the bun: basil-mayo sauce
-topped with green peppers and the grilled mushroom

requires no mustard, lol

I like to fill the burgers. I grill the mushrooms with garlic, olive oil, parsley, a tad bit of honey mustard, and chopped onion ahead of time and pop it in the fridge.

Then I mix ground chuck with, coco powder (browns the meat and adds a great taste, trust me) soy sauce, garlic butter, and season all.

Then I take the meat and flatten out thin pattys. On top of one thin patty I put cubed pepper jack cheese and my premaid mushroom onion mix. Then I fold over another thin patty on top. I seal the sides together with my hands.

My husband calls them hidden burgers. Bc he never knows what's inside. I make a lot of stuffed burgers all year. On the grill, in the oven, and on the stove top. =o)

Ok, the one detail that everybody misssed...it must be slightly burnt on the outside, so that you get just a bit of actual char on the burger itself. I'm talking *burnt*...that flavor, combined with the rest, is just...awesome.

Now I want lunch. See ya.