Preheat oven to 425°F. Grease an 8-inch square baking dish or spray with nonstick cooking spray; set aside.
In a large bowl, whisk together condensed soup, milk, chicken broth, thyme, salt, garlic powder, and pepper. Stir in mushrooms, raw chicken, and uncooked pasta.
Transfer mixture to prepared baking dish. Cover tightly with foil and bake for 35-40 minutes (until pasta is almost tender).
Remove foil and give everything a stir in the dish. Stir in sour cream, and sprinkle mozzarella cheese over top.
Return to the oven and bake, uncovered, for 5 more minutes, or until pasta is tender, chicken is cooked through, and cheese is melted.
Let the dish stand for about 5 minutes before serving.