Preheat oven to 350 degrees F. Crumble and cook sausage in medium skillet until browned. In large bowl, combine sausage, macaroni and cheese, mushrooms, tomatoes and green onions. Spoon into greased 2-quart casserole dish. Cover and bake for 30 minutes or until hot. Stir, sprinkle with parmesan cheese. Bake, uncovered for 5 minutes longer. Let stand for 10 minutes before serving.