Preheat your air fryer to 375°F (190°C) for 3 minutes.
In a large bowl, whisk together the melted butter, olive oil, minced garlic, Italian seasoning, onion powder, salt, and pepper.
Toss the halved mushrooms in the garlic butter mixture until every piece is well coated.
Arrange mushrooms in a single layer in the air fryer basket. Work in batches if needed — crowding them will steam rather than crisp them.
Air fry for 8–10 minutes, shaking the basket halfway through, until golden and slightly caramelized on the edges.
Transfer to a serving plate, sprinkle with fresh parsley and Parmesan (if using), and serve immediately.