In a 1-1/2-qt. microwave-safe dish, combine carrots and water. Cover and microwave on high for 4-6 minutes or until crisp-tender, stirring once; drain and return to dish.
In a bowl, combine the soup, cheese, onion, milk and mustard. Pour over carrots; stir to coat. Cover and microwave on high for 1-1/2 minutes. Toss the bread crumbs and butter; sprinkle over the top. Cover and microwave on high 1-1/2 minutes longer. Let stand for 2 minutes.