Lay a tortilla on a flat surface. Sprinkle 1/2 cup cheese on one half and spread 1 tablespoon salsa on the other half. Fold the tortilla over. Repeat with the remaining tortillas.
Place a filled tortilla in the air fryer basket or tray and brush lightly with melted butter.
Cook at 375 degrees Fahrenheit for 7-8 minutes, flipping halfway through to ensure both sides are browned evenly.
Repeat with the remaining tortillas and ingredients, brushing with more butter as necessary.
After cooking, remove the quesadilla and cut into wedges.
Serve with guacamole, sour cream, and additional salsa on the side.