Preheat your oven to 400°F (200°C) and lightly grease a 9×13-inch baking dish to prevent sticking.
Cut each chicken breast in half horizontally creating four thin cutlets. Pound any thicker parts gently to ensure even cooking.
In a bowl, whisk together one tablespoon of olive oil, minced garlic, Italian seasoning, salt, and black pepper before tossing in the chicken cutlets. Cover and refrigerate them for 15-30 minutes to absorb all those wonderful flavors.
Heat the remaining olive oil in a skillet over medium heat; add the fresh spinach and sauté for about 2-3 minutes until wilted before removing it from heat.
In a bowl, beat the softened cream cheese until smooth then stir in the wilted spinach along with half of the mozzarella cheese (and Parmesan if using) until well combined.
Arrange the marinated chicken in your prepared baking dish; spread the cream cheese mixture evenly over it then top everything off with the remaining mozzarella cheese before baking for 20-30 minutes until golden brown and bubbly.