Transfer beef with gravy to a large skillet (leave meat whole). Remove stems from shiitake mushrooms; halve or quarter mushrooms. Add mushrooms to skillet. Cover and cook over medium-low heat about 15 minutes or until heated through, stirring mushrooms once and turning roast over halfway through cooking time.
Use a wooden spoon to break meat into bite-size pieces. Stir onion dip into meat mixture; heat through (do not boil). Stir in hot cooked noodles. Makes 3 or 4 servings.