Preheat your oven to 400°F (200°C) and lightly grease a 9x13-inch baking dish.

Slice each chicken breast in half horizontally to create four thin cutlets. Gently pound thicker ends to achieve even thickness.

In a mixing bowl, whisk together 1 tablespoon olive oil, minced garlic, Italian seasoning, salt, and black pepper. Toss the chicken cutlets in this marinade, cover, and refrigerate for 15-30 minutes.

Heat the remaining olive oil in a skillet over medium heat. Add fresh spinach and sauté for 2-3 minutes until wilted. Remove from heat and set aside.

In a mixing bowl, beat softened cream cheese, then stir in the cooked spinach and 1/2 cup of mozzarella (Parmesan if using).

Optional: Sear marinated chicken in the skillet for 1-2 minutes per side for a deeper flavor.

Arrange the chicken cutlets in the greased baking dish, spread the cream cheese and spinach mixture over the top, and sprinkle with the remaining mozzarella cheese.

Bake for 20-30 minutes or until the chicken reaches an internal temperature of 165°F (75°C) and the cheese is melted and turns lightly golden.

Allow the casserole to rest for 5 minutes before serving.