Wash and dry the asparagus. Trim the woody ends (Note 3).
Place the spears in the basket of the air fryer. Rub well with the oil, salt, and pepper to coat all over. Arrange in a single layer.
Sprinkle with cheese if desired.
Air fry for 7 minutes, slightly longer (1-2 minutes) if the stalks are very thick. But make sure to check after 7 minutes already.
Serve immediately. You can sprinkle more cheese on top before serving.
Notes
Nutrition is calculated including the cheese.
Parmesan is not vegetarian, use a vegetarian hard cheese if desired. It is also optional; the air-fried asparagus tastes amazing with or without the cheese.
Freeze the trimmed ends and use them to make asparagus stock when you have enough of them. Or add to other homemade vegetable or meat stocks.