Preheat the air fryer to 400°F for 3 minutes while you prep the cauliflower.
Dry trimmed florets thoroughly on paper towels, then transfer to a large bowl and toss with cornstarch until lightly dusted.
Add olive oil, lemon pepper, garlic powder, onion powder, kosher salt, black pepper, lemon zest, and lemon juice; toss to coat evenly.
Arrange florets in a single layer in the air fryer basket without crowding; work in batches if needed.
Air fry at 400°F for 10–12 minutes, shaking the basket or flipping florets at 6 minutes, until edges are golden-brown and a fork meets slight resistance.
Transfer to a bowl, sprinkle chopped parsley and extra lemon zest, and serve immediately with an optional squeeze of lemon.