1. Brown the ground beef until cooked through, about 5 min. Drain. Add the onion and cook for 2 min. Add spaghetti sauce and mushrooms, set aside.
2. While ground beef is cooking, cook macaroni as directed on the package and drain.
3. Preheat oven to 350 degrees F. Spray a 9x13 baking dish. Layer half the pasta, half the meat mixture and half the sour cream in the baking dish. Layer provolone cheese over the top. Continue layering remaining pasta, meat mixture and sour cream. Sprinkle mozzarella cheese over the top. Cover loosely with foil sprayed with cooking spray.
4. Bake for 25 minutes. Uncover, bake for 5 minutes longer to brown the cheese slightly.