Combine spinach, cranberries, cream cheese, and mozzarella in a bowl.Slice a pocket into each chicken breast and season both sides.Stuff each pocket with the spinach cranberry mixture and secure with toothpicks.Heat olive oil in an oven safe skillet and sear chicken on both sides until golden.Transfer skillet to a 375°F oven and bake 18 to 22 minutes or until chicken reaches 165°F.Rest 5 minutes, remove toothpicks, and serve.