Add 1 tablespoon butter and panko crumbs to pan over medium heat.Cook while stirring until lightly toasted. Place in a dish and set aside.
Wipe mushrooms clean with a damp paper towel. Use a spoon to scrape and gently remove the gills underneath. Slice mushrooms 1/4" thick.
Sprinkle Panko crumbs over mushrooms (with parmesan cheese if using) and serve.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)