Preheat oven to 350 degrees
Hollow out each mushroom cap, reserving scraping
Cook and stir sausage and onion and reserved mushroom scaping until sausage is brown and cooked through 4-6 minutes. Drain and discard grease. Returning sausage mixture to pan
Stir in ⅓ cup parmesan cheese, bread crumbs, garlic, and parsley into the sausage mixture. Cook and stir until heated through 3-5 minutes
stuff each mushroom cap with sausage mixture and place on a baking sheet and the remaining parmesan on top
Bake stuffed mushrooms for 15 minutes
