Prep the chicken. Pat the chicken breasts dry. Use a sharp knife to slice a pocket into the side of each breast, keeping the opening small and the pocket deep. Don’t cut all the way through.
Season generously. Rub the outside of the chicken with olive oil. Sprinkle with salt, pepper, paprika, Italian seasoning, and onion powder on both sides. Set aside.
Make the filling. In a bowl, combine cream cheese, mozzarella, Parmesan, garlic, chopped spinach, a pinch of salt and pepper, and lemon zest if using. Mix until smooth and evenly combined.
Stuff the chicken. Spoon the spinach-cheese mixture into each pocket, pressing it in gently. Don’t overfill. Secure the opening with toothpicks to prevent leaks.
Preheat the air fryer. Set to 375°F (190°C) for 3–5 minutes. Lightly spray the basket with nonstick spray.
Cook the chicken. Place the stuffed chicken in the basket, seam side up. Air fry for 16–20 minutes, flipping once halfway. Cook until the thickest part reaches 165°F (74°C) on an instant-read thermometer.
Rest and serve. Let the chicken rest for 3–5 minutes to lock in juices. Remove toothpicks. Slice and serve warm.
