Preheat the air fryer to 400°F (200°C).
In a large mixing bowl, toss the cauliflower florets with vegetable oil, cornstarch, and salt until the surfaces are evenly coated in a thin film.
Arrange the cauliflower in the air fryer basket in a single layer, ensuring space between florets for optimal airflow.
Air fry for 15 to 18 minutes, shaking the basket at the 8-minute mark, until the edges are crispy and charred.
While cauliflower is frying, whisk gochujang, soy sauce, honey, rice vinegar, sesame oil, ginger, and garlic in a small saucepan.
Place the saucepan over medium heat and simmer for 2 to 3 minutes until the glaze thickens slightly and becomes glossy.
Transfer the crispy cauliflower to a clean bowl and pour the warm glaze over the florets, tossing gently to coat.
Return the coated cauliflower to the air fryer for an additional 2 minutes at 400°F to set the glaze and achieve a tacky consistency.
Garnish with toasted sesame seeds and sliced green onions before serving immediately.