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

Cut the chicken breasts in half horizontally, then pound to uniform thickness. Marinate with olive oil, minced garlic, Italian seasoning, salt, and pepper for 15 to 30 minutes.

Sauté the fresh spinach in a skillet with olive oil over medium heat for 2-3 minutes, until wilted.

In a mixing bowl, combine softened cream cheese, sautéed spinach, and half of the shredded mozzarella.

Optionally, sear the marinated chicken in a skillet for 1-2 minutes per side until golden brown.

Place the marinated chicken in the baking dish, spoon the creamy spinach mixture over it, and sprinkle with remaining mozzarella.

Bake for 20-30 minutes, ensuring the chicken reaches an internal temperature of 165°F (75°C) and the cheese is bubbling.

Let the casserole rest for 5 minutes before serving.