Preheat the oven to 400°F (200°C) and lightly grease a 9×13 inch baking dish with butter or cooking spray. Set aside.

Cut the chicken breasts in half horizontally to create four cutlets. Pound the thicker ends with a rolling pin for even thickness.

In a large mixing bowl, whisk together 1 tablespoon of olive oil, minced garlic, Italian seasoning, salt, and black pepper. Add the chicken cutlets and toss to coat. Cover and chill in the fridge for 15-30 minutes.

Heat the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add the spinach and cook, stirring frequently until wilted, about 2-3 minutes. Set aside.

In a medium bowl, beat the cream cheese until smooth. Add the wilted spinach, 1/2 cup of mozzarella, and Parmesan cheese (if using). Mix until well combined.

Remove the chicken from the marinade, letting the excess drip off. For added texture, sear the chicken in the skillet for 1-2 minutes per side if desired.

Arrange the chicken cutlets in a single layer in the prepared baking dish. Spread the spinach and cream cheese mixture over the chicken and sprinkle the remaining mozzarella cheese on top.

Bake for 20-30 minutes, or until the chicken is cooked through and the cheese is melted and lightly browned. Let stand for 5 minutes before serving.