01 - Preheat the oven to 400°F. Lightly grease a baking dish with cooking spray or a small amount of olive oil.
02 - In a mixing bowl, combine crumbled feta cheese, chopped spinach, minced garlic, cream cheese, dill (if using), salt, and black pepper. Mix thoroughly until all ingredients are evenly distributed and the mixture forms a cohesive filling.
03 - Using a sharp knife, slice a horizontal pocket into the side of each chicken breast, cutting carefully to create a deep cavity without cutting completely through to the other side.
04 - Generously fill each pocket with the spinach and feta mixture. Secure the opening with toothpicks to prevent filling from escaping during cooking.
05 - Rub the exterior of each stuffed chicken breast with olive oil. Season generously with additional salt and freshly ground black pepper.
06 - Arrange the stuffed chicken breasts in the prepared baking dish, leaving space between pieces for even cooking. Bake for 25-30 minutes, or until the chicken reaches an internal temperature of 165°F and the juices run clear when pierced.
07 - Carefully remove the toothpicks from each breast. Transfer to serving plates and accompany with fresh lemon wedges for squeezing over the chicken.