Preheat the air fryer to 350°F (175°C)
Slice each croissant in half horizontally
Spread a thin layer of Dijon mustard inside each croissant if desired
Place two slices of ham inside each croissant
Add one slice of cheese over the ham
Close the croissants gently
Brush the tops with melted butter
Sprinkle dried thyme or Italian seasoning on top
Place croissants in the air fryer basket in a single layer
Air fry until the croissants become golden and the cheese melts
Remove carefully and allow to cool slightly before serving