Preheat the air fryer to 360°F (182°C) for 3-5 minutes.
Prepare the chicken breasts: Pat chicken breasts completely dry with paper towels. Using a sharp knife, carefully slice horizontally through the thickest part of each breast to create a deep pocket, cutting about three-quarters of the way through while leaving one edge intact.
Make the filling: In a medium bowl, combine the ricotta cheese, chopped spinach, mozzarella, Parmesan cheese, minced garlic, Italian seasoning, and red pepper flakes (if using). Mix until well blended and season generously with salt and pepper to taste.
Stuff the chicken: Divide the filling mixture evenly among the four chicken breasts, using about ¼ to ⅓ cup per breast. Spoon the mixture into each pocket, packing gently but firmly. Secure the opening with 2-3 toothpicks inserted diagonally to create a seal.
Season the exterior: In a small bowl, combine paprika, garlic powder, onion powder, oregano, salt, and pepper. Brush each stuffed chicken breast lightly with olive oil on all sides. Sprinkle the seasoning mixture generously over the entire surface of each breast, including the sides, and pat gently to help it adhere.
Air fry: Lightly spray the air fryer basket with cooking spray. Place the stuffed chicken breasts in the basket in a single layer, leaving space between each piece. Cook at 360°F for 18-22 minutes, flipping the chicken breasts halfway through (around the 10-minute mark) for even browning.
Check for doneness: The chicken is done when it reaches an internal temperature of 165°F (74°C) when measured with an instant-read thermometer inserted into the thickest part of the meat. The exterior should be golden brown and crispy.
Rest and serve: Transfer the cooked chicken breasts to a clean plate and tent loosely with aluminum foil. Let them rest for 4-5 minutes before removing toothpicks and slicing or serving. This allows the juices to redistribute throughout the meat for maximum tenderness.