Combine panko, onion and garlic powders, cayenne, and salt in a shallow bowl or pie plate. In another shallow bowl, beat the egg. One by one, dip florets into the egg and then into the breadcrumb mixture. Place on a large plate or tray. Drizzle with olive oil.
Arrange the cauliflower in the basket of the air fryer in a single layer leaving a little space between each. Do not over-crowd, work in batches if necessary.
Air fry for 10 - 12 minutes or until crisp. Toss with hoisin sauce and sprinkle with sesame seeds and green onion. Serve with extra hoisin sauce for dipping if desired.