Start by heating the olive oil in a large skillet over medium heat. Season your chicken breasts with Italian seasoning, salt, and pepper, then cook until golden brown on both sides and fully cooked through. Once done, slice the chicken into bite-sized pieces and set aside.
In the same skillet, add the minced garlic and sauté for about 1 minute, or until fragrant. This step adds a rich aroma to the dish, enhancing the flavors of the chicken and spinach.
In a mixing bowl, combine the softened cream cheese, sour cream, mozzarella cheese, and Parmesan. Stir everything together until smooth. Add salt and pepper to taste, then mix in the sautéed garlic and cooked chicken. This creamy base will form the rich, savory foundation of your casserole.
Next, layer the fresh spinach over the creamy chicken mixture. Fresh spinach is a great choice because it wilts beautifully, adding color and nutrition without the excess moisture that frozen spinach can bring. Gently mix the spinach into the chicken and cream cheese mixture.
Transfer the chicken-spinach mixture into a greased 9x13-inch baking dish. Spread it out evenly, then bake at 350°F for 25-30 minutes. The casserole is done when it’s bubbly and golden on top.