Place the shrimp in a bowl, cover with buttermilk and refrigerate for 15 minutes.
Whisk the flour, cornstarch, garlic powder, paprika, salt and pepper in a shallow bowl.
Lift the shrimp from the buttermilk, let the excess drip off, and toss in the flour mixture. Shake off the extra.
Preheat the air fryer to 400°F for 3 to 5 minutes.
Spray the basket, add the shrimp in a single layer and spray until no dry flour shows. Air fry 4 minutes.
Flip, spray any dry spots and air fry 3 to 4 minutes more, until golden and opaque inside. Repeat with remaining shrimp.
Whisk all sauce ingredients until smooth.
Toss the hot shrimp in the sauce, garnish with green onions and sesame seeds, and serve immediately.