Preheat air fryer to 360°F for 5 minutes. Toss cauliflower with cornstarch, oil, garlic powder and onion powder in a large bowl until well coated. Generously coat with cooking spray and toss again. Working in batches if necessary, arrange the cauliflower in a single layer in the air-fryer basket. Cook until the edges are golden and crispy, about 10 minutes.