Preheat oven to 350 degrees F (175 degrees C). Grease a 1-quart casserole dish.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
In a mixing bowl, combine mushroom soup, milk, salt, and pepper. Mix thoroughly. Then add tuna, mushrooms, and pasta. Mix thoroughly. Pour mixture into the greased casserole dish.
In another mixing bowl, combine bread crumbs, butter, and thyme. Mix well. Sprinkle over the top of the tuna mixture.
Bake uncovered in a preheated oven until bubbling and golden brown, about 40 minutes.
