Finely chop or pulse the 600 g chicken breast. Mix with the mustard, paprika, cayenne, garlic powder, onion powder, ½ teaspoon salt, black pepper and celery powder. Divide into six equal 100 g patties.
Crush 50 g cornflakes and keep up to 10 g more ready if needed. Press the crumbs onto both sides of each patty.
Pour enough hot sauce into a shallow dish to dip and coat each cornflake-covered patty. Work gently so the coating stays in place. Discard any sauce that touches raw chicken.
Lightly spray the air-fryer basket and both sides of the patties. Arrange in a single layer and cook in batches at 390°F (200°C). Start checking after 10 minutes; continue until each patty reaches 165°F (74°C) at the center.
Taste one cooked patty and add more salt only if needed. Toast the six buns if desired.
Place one patty on each bun with shredded romaine and 7 g light mayonnaise. Close the sandwiches and serve.
