Trim the woody ends from the asparagus by snapping one spear and using it as a guide for the rest.
If the asparagus is very thick, peel the lower third with a vegetable peeler.
Pat the asparagus dry well with paper towels.
Toss the spears with olive oil, salt, black pepper, and garlic powder.
Preheat the air fryer to 390°F for 2 to 3 minutes if desired.
Arrange the asparagus in a single layer with only slight overlap.
Air fry at 390°F for 6 to 8 minutes, tossing once at the 4-minute mark.
Thin spears usually finish in about 6 minutes, while thick spears may need 8 to 9 minutes.
Finish with lemon juice and optional Parmesan, then taste and adjust salt before serving.