Begin by cutting your sirloin steak into bite-sized cubes, placing them in a large bowl. Pour in the low sodium soy sauce, brown sugar, garlic powder, and ground black pepper. Combine all ingredients thoroughly and let the steak marinate at room temperature for 20 to 30 minutes.

As the steak marinates, preheat your air fryer to 400°F (200°C). This usually takes around 5 minutes.

Once marinated, arrange the steak bites in the air fryer basket in a single layer, avoiding overlapping. Use cooking spray to lightly coat the basket beforehand.

Set the timer for 4 to 6 minutes, cooking the steak bites until they reach your desired doneness, shaking the basket halfway through.

After cooking, remove the steak bites from the air fryer and let them rest for about 5 minutes before serving.