Place potatoes and water in a microwave-safe dish. Cover and microwave on high for 8-10 minutes or until tender. Meanwhile, in a large skillet, cook beef over medium heat until no longer pink; drain. Stir in garlic powder and onion powder.
Prepare gravy according to package directions. Place the potatoes in a mixing bowl; add milk, butter, salt and pepper. Beat on medium speed until smooth (or use a potato masher). Serve beef and gravy over mashed potatoes.