Trim the stem ends from 1 pound of Brussels sprouts and remove any loose, yellow, or damaged outer leaves. Cut larger sprouts in half; very small sprouts may be left whole or halved.

Pat the Brussels sprouts very dry with clean kitchen towels or paper towels. Toss them with 1 tablespoon olive oil, 1/2 teaspoon kosher salt, 1/4 teaspoon black pepper, and 1/2 teaspoon garlic powder until every piece is evenly coated.

Preheat the air fryer to 375°F–400°F, following the temperature that suits your model. Arrange the sprouts mostly in a single layer with the cut sides facing down, leaving space around them for hot air to circulate.

Cook at 375°F for about 14–18 minutes or at 400°F for about 10–14 minutes. Shake the basket or turn the sprouts halfway through, then continue cooking until the cut sides are deeply browned and the centers are tender.

Transfer the hot Brussels sprouts to a serving bowl and taste for seasoning. Finish with 1–2 teaspoons lemon juice, 1 tablespoon Parmesan, 1 tablespoon balsamic glaze, a pinch of red pepper flakes, or additional salt as desired.