Toss the cauliflower florets with cornstarch, salt, and white pepper in a large bowl until evenly coated. Spray generously with cooking spray and toss again.
Preheat the air fryer to 400F. Arrange the cauliflower in a single layer and air fry for 15-18 minutes, shaking the basket every 5 minutes, until deeply golden and crispy on the edges.
While the cauliflower cooks, make the sauce. Whisk together the soy sauce, rice vinegar, honey, hoisin sauce, cornstarch, and water.
Heat sesame oil in a small saucepan over medium heat. Add the garlic, ginger, and red pepper flakes and cook for 30 seconds until fragrant. Pour in the sauce mixture and stir constantly until it thickens, about 2-3 minutes.
Transfer the crispy cauliflower to a large bowl, pour the sauce over, and toss gently to coat. Top with green onions and sesame seeds and serve immediately over steamed rice.