Wash mushrooms then remove and chop up stems. Cook chopped mushroom stems in butter for 5 minutes. Add the onion, garlic, salt, and pepper then cook for another 1 to 2 minutes
Transfer the mushroom mixture to a mixing bowl and then let it cool slightly. Add the cream cheese, parmesan, and parsley then stir until well combined.
Spray the air fryer basket with oil then add the stuffed mushrooms.
Spray evenly with another coating of oil then cook in the air fryer at 390 degrees for 8 minutes.