Begin by buttering one slide of each piece of bread. Evenly sprinkle parmesan cheese on top.
Flip one piece over. Layer 2 slices of cheese on the bread. Next, layer your leftover pot roast on top of the cheese slices.
Top with another slice of cheese, then layer with caramelized onions.
Top with your other slice of bread, butter side up.
Place in the air fryer at 350°F for 5 minutes on one side.
After 5 minutes, flip and cook an additional 4 minutes, or until golden brown. Serve and enjoy!