A real good way to do it is to saute some think-sliced shiitakes and creminis in a pan with salt, pepper, and a shallot; once you get a good fond, put the shrooms in between two slices of bread with a bit of cheese (fresh mozzarella is a good one here, so is gruyere), deglaze the pan with butter, and then throw the sandwich in the pan until it's done the way you like your grilled cheese.

I call it "beyond beyond meat."