In 10-inch skillet, melt butter over high heat. Add chicken, onion and mushrooms; cook 3 to 5 minutes, stirring occasionally, until outside of chicken turns white.
Stir in contents of sauce mix pouch (from Chicken Helper box), hot water, milk and mustard. Heat to boiling, stirring occasionally. Stir in contents of uncooked pasta pouch (from Chicken Helper box); reduce heat. Cover; simmer about 10 minutes, stirring frequently, until pasta is tender.
Stir in asparagus. Cover; cook 2 minutes, stirring occasionally. Remove from heat. Uncover; let stand about 5 minutes or until sauce is as thick as you'd like (sauce will thicken as it stands). Stir before serving.