Carefully remove the stems from the mushrooms. Finely chop the stems and set them aside.
Place a large skillet over medium heat. Cook the sausage, breaking it up into small pieces, until browned through, about 10 minutes.
Once the sausage is browned add in the mushroom stems and cook for 2-3 minutes. Add the green onions and garlic to the skillet and cook another 1-2 minutes.
Add the cream cheese and Parmesan cheese to the sausage mixture and stir until melted and evenly combined. Stir in the breadcrumbs and remove the skillet from the heat.
Scoop a heaping tablespoon of filling into the mushrooms. Place onto a foil-lined baking sheet.
Bake for 10 to 15 minutes or until the filling is browned and the mushrooms are softened.
Remove from the oven. Garnish with chopped parsley, if desired, and serve warm.
Notes
If you want to give your mushrooms a kick, use hot breakfast sausage instead of regular/mild sausage.
You can use the 1 lb. chub of sausage or links. If you use links, remove the casings before adding the sausage to the skillet.