Heat the oven to 400°F. Lightly grease a 9x13-inch baking dish with butter or nonstick cooking spray and set it aside.

Slice each chicken breast horizontally to make 4 thinner cutlets in all. Pound the thicker parts gently with a rolling pin so the chicken is an even thickness.

In a large bowl whisk 1 tablespoon of the olive oil with the garlic, Italian seasoning, salt and pepper. Add the cutlets and turn them until they are evenly coated. Cover and refrigerate for 15 to 30 minutes.

Heat the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add the spinach and cook, stirring often, for 2 to 3 minutes, until wilted. Take the skillet off the heat and set the spinach aside.

In a medium bowl beat the softened cream cheese until smooth. Mix in the cooked spinach, 1/2 cup of the mozzarella and the Parmesan, if using, until well combined and creamy.

Lift the chicken from the marinade and let the extra drip off. If you like, sear the cutlets in a skillet for 1 to 2 minutes per side. Lay them in a single layer in the baking dish.

Spread the spinach and cream cheese mixture evenly over the chicken and sprinkle the remaining 1/2 cup of mozzarella on top. Bake for 20 to 30 minutes, until the chicken reaches 165°F on a food thermometer and the cheese has melted and turned lightly golden.

Let the casserole rest for 5 minutes before serving.