Preheat the Oven:
Preheat your oven to 400°F (200°C). Lightly grease a 9×13-inch baking dish with butter or cooking spray.

Prepare the Chicken:
Slice each chicken breast in half horizontally to make four thin cutlets. Lightly pound thicker ends to ensure even cooking.

Marinate:
In a large bowl, whisk together 1 tablespoon olive oil, garlic, Italian seasoning, salt, and pepper. Add chicken and toss to coat. Cover and refrigerate for 15–30 minutes.

Cook the Spinach:
Heat the remaining olive oil in a skillet over medium heat. Add spinach and cook until wilted (2–3 minutes). Set aside.

Mix the Filling:
In a medium bowl, beat softened cream cheese until smooth. Stir in cooked spinach, ½ cup mozzarella, and Parmesan (if using).

Optional – Sear the Chicken:
For extra flavor, sear marinated chicken in a hot skillet for 1–2 minutes per side until lightly golden.

Assemble the Casserole:
Arrange chicken in the prepared baking dish. Spread the cream cheese and spinach mixture evenly over the top. Sprinkle with remaining mozzarella cheese.

Bake:
Bake uncovered for 20–30 minutes, or until chicken reaches an internal temperature of 165°F (75°C) and cheese is melted and lightly browned.

Serve:
Let rest for 5 minutes before serving. Pair with a side salad, roasted vegetables, or pasta for a complete meal.