Preheat your Blackstone to medium heat. Add cooking oil of choice, onions, mushrooms, chicken, kosher salt, pepper, and Italian seasoning. Cook 6 to 7 minutes, mixing with spatulas a few times.
Add garlic and spinach, cook 2 to 3 more minutes.
Add sun-dried tomatoes, mozzarella, parmesan, and heavy cream. Mix with spatulas, containing the cream until it thickens into a sauce. Add more kosher salt, pepper, and Italian seasoning and cook 1 more minute.