Spread the mayonnaise on one side of each of the slices of bread. Place two slices of bread in the air fryer basket, mayo side facing down. Divide the shredded cheese over the tops of the two slices of bread. Cover the cheese with the remaining slices of bread, mayo side up.
Set the air fryer to 350°F for 6 to 8 minutes, or until the cheese is melted and the bread is crispy – it may not brown all that much. Cut in half and serve hot.