Lightly grease a baking pan with cooking spray. Set aside.
Slide the Air Fryer Basket inside and adjust the temperature to 350 °F to preheat for 5 minutes.
In a bowl, add spinach, onion, garlic, cream cheese, nutmeg, salt, and black pepper and mix well.
Place spinach mixture into the prepared baking pan.
After preheating, arrange the baking pan into the Air Fryer Basket.
Slide the basket into Air Fryer and set the time for 10 minutes.
After 10 minutes of cooking, top the spinach mixture with Parmesan.
Immediately adjust the temperature to 400 °F for 5 minutes.
After cooking time is finished, remove the baking pan from Air Fryer and serve.