Preheat the oven to 350°F (175°C) and spray a 9x13-inch baking dish with nonstick cooking spray.
Boil the spaghetti in a large pot of salted water until cooked al dente. Drain and set aside.
Melt the butter in a large skillet over medium heat. Add the mushrooms and cook for about 5 minutes or until they are tender and browned.
In a large bowl, mix the cream of mushroom soup, chicken broth, sour cream and parmesan cheese.
Add the shredded chicken, cooked mushrooms and cooked spaghetti to the bowl. Mix until the pasta is completely coated in the sauce, then transfer to the baking dish.
Evenly distribute the mozzarella cheese on top of the casserole. Bake for 30 minutes or until the casserole is bubbling and the cheese is melted.
*Nutritional information is a calculated guesstimate. Please note that this can change with different brands and modifications you may make to the recipe. For the most accurate information, use a nutritional calculator with the exact brands and measurements you're using with each recipe.