Preheat air fryer to 375°F (190°C).
Wash Brussels sprouts under cool running water, path them dry and add to a bowl. Using a knife, carefully trim the stems and cut each Brussel sprout lengthwise into 2 halves. Transfer back to the bowl, once halved.
Add olive oil, kosher salt, ground black pepper and optionally garlic powder to the vegetables, then toss to combine.
Transfer seasoned Brussels sprouts to the air fryer basket, without overcrowding it. If necessary, air fry in multiple batches.
Air fry Brussels sprouts for 10 to 12 minutes, shaking halfway through cooking time. Remove from the air fryer basket and serve.