Grease 2 ramekins with cooking spray. Set aside.
In a non-stick wok, melt butter over medium heat and cook onion and mushroom for about 3 minutes.
Add spinach and cook for about 2-3 minutes.
Remove the wok of mushroom mixture from heat and set aside to cool slightly.
Meanwhile, in a small-sized bowl, add eggs, rosemary, salt and black pepper and whisk well.
Divide the beaten eggs into the prepared ramekins evenly and top with the veggie mixture, followed by the cheese.
Slide the Air Fryer Basket inside and adjust the temperature to 330 °F to preheat for 5 minutes.
After preheating, arrange the ramekins into the Air Fryer Basket.
Slide the basket into Air Fryer and set the time for 12 minutes.
After cooking time is finished, remove the ramekins from Air Fryer and place onto a wire rack for about 5 minutes before serving.