Place carrots in a saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook until tender. Meanwhile, in a small skillet, saute onion in butter until tender.
Drain carrots; add onion, soup, mushrooms and Parmesan cheese.
Transfer to a greased 2-1/2-qt. baking dish.
Sprinkle with bread crumbs.
Bake, uncovered, at 350° for 30-35 minutes or until heated through.