Clean and remove the stems from the mushrooms.
Combine chopped stems, breadcrumbs, cheeses, cream cheese, garlic, parsley, olive oil, salt, and pepper in a bowl.
Stuff each mushroom with the mixture and top with extra cheese if desired.
Grill over medium heat or bake at 375°F for 8-10 minutes (grill) or 12-15 minutes (oven).
Serve hot, garnished with parsley.