Start by draining the tuna, and then pour it into a medium-sized mixing bowl, add the onions.
Add in the celery.
Mix in the mayonnaise,
Smear the tuna salad on top of the bread, then top with a slice of cheese. And then place it on an air fryer safe tray or in the air fryer basket. Set the temperature to 250 degrees F, for 4 minutes.
Plate, serve and enjoy!