On the tortilla to the left, spread the salsa on it. On the tortilla on the right, add mozzarella cheese, Mexican cheese, chicken, red bell peppers, and onions.
Place the tortilla with the salsa on top of the cheese/chicken one. Press down quite firmly to prevent it from flipping off in the air fryer.
Brush the tops of the tortilla with melted butter.
Place the tortilla in the air fryer basket and cook for 4-5 minutes, or until lightly golden brown.
Remove the quesadilla from the air fryer basket and cut it into 4 portions.