Yep. You can put anything on portabella buns! I made a household favorite last night for the fam; toasted ham/Swiss sandwiches. I didn’t want to miss out, so I made mine on the mushrooms. Ohhhh it was GOOD! Even cold, because I got called away before I could eat.
Ham, Swiss cheese, sliced onions, stone ground mustard, a dash of horseradish, thinly sliced tomatoes, black pepper and garlic powder.
On the bun ones I make for the fam, I put a little mayo on the bread for moisture. The portabella doesn’t need extra, since when it wilts it has more moisture.
400 degree oven preheated. Lay the “bun” halves face up and layer on the stuff. On one side I put on the mayo, mustards, seasoning, meat and tomatoes. On the other side I put the onions and then the cheese. Toast it until the mushrooms are wilted and/or the buns are toasty on the bottom and the cheese is melted. Put together and ENJOY! I added a nice Greek salad to fill the plate.