Begin by rinsing the Brussels sprouts thoroughly under cool water to remove any dirt. Slice them in half vertically for even cooking. Place in a mixing bowl.

Set your Ninja Grill to air crisp mode at 400°F (204°C) and preheat for approximately 5 minutes.

In the bowl, drizzle olive oil and balsamic vinegar, then sprinkle with kosher salt and black pepper. Toss well until all sprouts are coated.

Arrange the seasoned Brussels sprouts in a single layer in the air crisp basket. Cook for 20 minutes, tossing every 5 minutes.

After 20 minutes, check for doneness. They should be golden-brown and fork-tender. Cook an additional 2-3 minutes if needed.