Preheat your oven to 400°F (200°C). Grease a 9×13-inch baking dish.

Slice chicken breasts horizontally to create thin cutlets. Marinate with olive oil, minced garlic, Italian seasoning, salt, and black pepper for 15-30 minutes.

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

Beat cream cheese in a bowl until smooth. Fold in sautéed spinach and half a cup of shredded mozzarella cheese.

Optionally, sear marinated chicken cutlets in the skillet for 1-2 minutes on each side.

Lay marinated chicken cutlets in the greased baking dish and cover with the creamy spinach mixture. Sprinkle remaining mozzarella cheese on top.

Bake in the preheated oven for 20-30 minutes until bubbly and golden. Check that chicken reaches an internal temperature of 165°F (75°C).

Let the casserole rest for 5 minutes before serving.