Preheat the air fryer: Set to 390–400°F (200°C). A hot basket helps the bacon crisp quickly.
Prep the asparagus: Snap or trim off the woody ends.
Pat dry so oil and seasoning stick well.
Season: In a bowl, toss asparagus with olive oil, salt, pepper, and garlic powder if using.
Arrange in the basket: Place the asparagus in the air fryer basket in a mostly single layer. Scatter bacon pieces evenly over the top so they render onto the spears.
Cook: Air fry for 7–10 minutes, shaking or tongs-tossing halfway. Thinner spears and thinner bacon cook faster; start checking at 7 minutes.
Check doneness: Asparagus should be bright green with a few browned edges and tender when pierced.
Bacon should be browned and crisp. If needed, cook 1–2 minutes more.
Finish: Transfer to a serving plate. Add lemon zest and a squeeze of lemon juice.
Sprinkle parmesan if you like. Taste and adjust salt.
Serve: Enjoy right away for the best texture.