01 - Preheat the oven to 375°F. Lightly grease a baking dish with cooking spray or a small amount of olive oil.
02 - Heat 1 tablespoon olive oil in a large skillet over medium heat. Add minced garlic and sauté for 30 seconds until fragrant. Add chopped spinach and cook, stirring constantly, until wilted, about 2 to 3 minutes. Remove from heat and let cool slightly.
03 - In a mixing bowl, combine the sautéed spinach, crumbled feta cheese, chopped fresh dill, dried oregano, ground nutmeg, and lemon zest. Mix thoroughly until all ingredients are evenly distributed.
04 - Using a sharp knife, carefully cut a horizontal pocket into the side of each chicken breast, slicing about three-quarters of the way through without cutting completely to the other side.
05 - Season each chicken breast thoroughly inside and out with salt and freshly ground black pepper, ensuring even coverage on all surfaces.
06 - Divide the spinach-feta mixture evenly among the four chicken breasts, stuffing each pocket with the filling. Secure the opening by inserting toothpicks or tying with kitchen twine to prevent filling from escaping during cooking.
07 - Heat 1 tablespoon olive oil in the skillet over medium-high heat. Place stuffed chicken breasts in the hot pan and sear for 2 to 3 minutes per side until golden brown and slightly crisped.
08 - Transfer seared chicken breasts to the prepared baking dish. Bake for 20 to 25 minutes, or until the chicken is completely cooked through and reaches an internal temperature of 165°F when tested with a meat thermometer.
09 - Remove the baking dish from the oven. Carefully remove all toothpicks or kitchen twine before serving. Let the chicken rest for 5 minutes to allow juices to redistribute.