Hmm. Diluting the air will be the hardest thing: A run off the mill heat gun will do 600C at 2000W in a concentrated stream, if you regulate it down to air frying temperature you'll get very little total power so you'll want to cool it down by pulling in additional ambient air instead. But with that out of the way... add a metal box and a timer? The heat gun already regulates the temperature. Probably not via PID though, just pre-set power levels for coils and fan they're not exactly precision instruments.

...and all that made me wonder and apparently there's no culinary heat guns which would be a smart choice because they'd pay attention for all materials to be food-safe. But there are hobbyists reporting great results using standard heat guns instead of the usual torch. Not, to be honest, that you'd expect standard lighter gas to be food-grade, of course.