1. Place macaroni and water in 2-quart casserole. Cover tightly and microwave on high (100%) to boiling, 4 to 5 minutes. Let stand 5 minutes. (Macaroni will continue to cook and absorb most of water while it stands.)
2. Stir in milk, flour and mustard. Fold in zucchini, cheese and dried beef. Cover tightly and microwave on high (100%) 4 minutes; stir. Cover and microwave until mixture is bubbly and macaroni is tender, 3 to 4 minutes longer.