Slice a pocket into each chicken breast carefully without cutting through completely, ensuring enough space for filling.
Mix spinach, cream cheese, mozzarella, garlic, sun-dried tomatoes, and seasoning until smooth and well combined.
Stuff each chicken breast evenly and secure with toothpicks or twine to keep the filling inside during cooking.
Rub chicken with olive oil and season generously to enhance flavor and create a tasty outer layer.
Sear chicken in a hot skillet until golden on both sides to build flavor before baking.
Bake at 375°F (190°C) until fully cooked and juicy, then allow it to rest before serving.