01 - Preheat oven to 400°F. Lightly grease a baking dish with cooking spray or a small amount of oil.
02 - Heat a skillet over medium heat. Add chopped spinach and cook for 1-2 minutes until wilted. Transfer to a bowl and let cool slightly. Add feta, cream cheese, garlic, parsley, oregano, and nutmeg. Mix until well combined.
03 - Pat chicken breasts dry with paper towels. Using a sharp knife, cut a horizontal pocket into the side of each breast, being careful not to cut through completely. Season both sides with salt and pepper.
04 - Divide the spinach and feta mixture evenly among the chicken breasts, stuffing it into each pocket. Secure the opening with toothpicks if needed.
05 - Place stuffed chicken breasts in the prepared baking dish. Drizzle with 1 tablespoon olive oil.
06 - Bake for 25-30 minutes, or until the chicken is cooked through (internal temperature reaches 165°F) and juices run clear.
07 - Remove toothpicks before serving. Serve hot alongside roasted vegetables, salad, or rice.