If those large hamburger sized mushrooms you are talking about are
portobello mushrooms - I like to do the following:
Marinate the mushrooms, after brushing and taking off the stems, in a
mixture of barbeque sauce (about 2 to 3 Tbs.), lemon juice (@ 1 tsp.) and a
little fatfree salad dressing (like a wine vinaigrette - @ 1 Tbs.) for about
5 minutes. I do this by brushing the mixture on the top side of the
mushroom, putting them in a dish gill side up or whatever you call the
underside of this mushroom. I pour and brush the rest of the marinade on to
this side. Cover the dish with plastic wrap, venting a corner. For two large
mushrooms microwave on high for 5 minutes. Put on hamburger buns and pour
the marinade in the bottom of the dish over the mushrooms. Really good!
Patty in AZ