Remove from the oven and using tongs, gently flip the caps over, stem side up.
Spoon 2 tablespoon of pizza sauce into each cap. You can add more if you like.
Place the prosciutto on top of the sauce.
Evenly divide the shredded cheeses over top the meat.
Place the shaved Parmesan on top of the cheeses.
Place some of the pepper rings on top followed by the oregano.
Place back in the oven for 10-15 minutes or until the cheeses are all melted and the mushroom is tender but still slightly firm (you want this to be a crust that you can cut with a knife).