Prepare the Chicken: Pat the chicken breasts completely dry with paper towels. Place one chicken breast on a cutting board and place your palm flat on top. Using a sharp knife, carefully slice horizontally through the thickest part of the breast, creating a pocket. Be careful not to cut all the way through—you want to create a "book" that opens up. Repeat with remaining chicken breasts.
Make the Filling: In a medium bowl, combine softened cream cheese, shredded mozzarella, chopped spinach, sun-dried tomatoes, and minced garlic. Mix until well combined. The mixture should be spreadable but not too loose.
Stuff the Chicken: Open each butterflied chicken breast like a book. Spoon 3-4 tablespoons of the filling mixture onto one side, leaving about a half-inch border around the edges. Fold the chicken closed and secure with 3-4 toothpicks along the open edge, making sure the toothpicks go through both layers of chicken.
Season the Outside: Brush the outside of each stuffed chicken breast with olive oil. In a small bowl, mix together garlic powder, onion powder, paprika, Italian seasoning, salt, and pepper. Sprinkle the seasoning mixture generously over both sides of each chicken breast, pressing gently so it adheres.
Preheat Air Fryer: Preheat your air fryer to 375°F for 3-5 minutes.
Air Fry: Place the stuffed chicken breasts in the air fryer basket in a single layer, making sure they don't touch. Cook for 16-18 minutes, flipping halfway through at the 8-9 minute mark, until the internal temperature reaches 165°F when checked with a meat thermometer in the thickest part (not the filling). The chicken should be golden brown and juices should run clear.
Rest and Serve: Remove the chicken from the air fryer and let it rest for 5 minutes. This allows the juices to redistribute throughout the meat. Carefully remove all toothpicks (wetting them first makes them slide out more easily), slice if desired, and serve immediately. Enjoy!