Carefully remove mushroom stems and chop them finely; set aside.

In a medium skillet, brown the sausage until it’s almost completely browned, then stir in the chopped mushrooms and onion. Sauté for 2-3 minutes, until tender.

Add the garlic and red pepper flakes and saute for another 30 seconds, until fragrant. Drain the excess grease, and aside to cool completely.

In a medium sized bowl, add cream cheese and egg yolk, stirring well to combine. Stir in the Parmesan, bread crumbs, and parsley. Fold in the cooled sausage and onion mixture until well mixed. Season to taste with salt and pepper.

Use a spoon to stuff each mushroom cap with the filling, making a small mound on the top.

Spray the inner basket of an air fryer with cooking spray. Place the stuffed mushrooms in the basket and air fry at 390 degrees for 5-7 minutes, or until golden on top, cooking in batches as needed.