01 - Preheat the oven to 375°F.
02 - In a medium bowl, combine spinach, feta cheese, cream cheese, garlic, dill, nutmeg, and red pepper flakes. Mix until well incorporated.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, carefully cut a horizontal pocket into the thickest side of each breast without cutting through completely.
04 - Season the interior and exterior of each chicken breast generously with salt and black pepper.
05 - Fill each pocket with the spinach-feta mixture. Secure openings with toothpicks to prevent filling from escaping during cooking.
06 - Heat 1 tablespoon olive oil in a large oven-safe skillet over medium-high heat. Sear stuffed chicken breasts for 2-3 minutes per side until golden brown.
07 - Drizzle with remaining olive oil. Transfer skillet to preheated oven and bake for 20-25 minutes until internal temperature reaches 165°F.
08 - Remove toothpicks carefully. Let chicken rest for 5 minutes before serving to allow juices to redistribute.