In a large saucepan, saute the shrimp, mushrooms, garlic powder, salt and pepper in butter for 3-5 minutes. Stir in the fettuccine, cheese, milk and sour cream. Cook over medium heat for 3-5 minutes or until heated through (do not boil). Sprinkle with parsley if desired.
Editor's note: Scallops or crab may be substituted for half of the shrimp.