Spread a thin layer of mayonnaise on the outside of both pieces of bread.
Place cheese slices inside and close the sandwich and place in the air fryer basket. Place a couple toothpicks in each sandwich to ensure the top slice of bread stays in place while in the air fryer.
Cook for 6-8 minutes, flipping halfway through, or until the bread is golden on the outside and cheese is melted.
Notes
Depending on the brand of air fryer, you may need to use a toothpick to hold the top bread in place until the cheese melts.