01 - Preheat oven to 400°F and lightly grease a baking dish with cooking spray or olive oil.
02 - Combine crumbled feta, chopped spinach, minced garlic, cream cheese, fresh dill, salt, and pepper in a mixing bowl. Mix thoroughly until evenly distributed.
03 - Using a sharp knife, slice a horizontal pocket into the thickest part of each chicken breast, being careful not to cut completely through to the other side.
04 - Generously fill each pocket with the spinach-feta mixture. Secure openings with toothpicks to prevent filling from escaping during cooking.
05 - Rub olive oil evenly over the outside of each breast and season generously with salt and black pepper.
06 - Arrange stuffed chicken breasts in the prepared baking dish and bake for 25 to 30 minutes, or until internal temperature reaches 165°F and juices run clear.
07 - Remove toothpicks carefully. Serve immediately with fresh lemon wedges on the side for squeezing over the chicken.