Heat oven to 375°F. Spray 3-quart casserole with nonstick cooking spray. Cook egg noodles as directed on package. Drain; cover to keep warm.
Meanwhile, in 12-inch nonstick skillet, cook ground beef, mushrooms and garlic over medium-high heat for 5 to 7 minutes or until beef is thoroughly cooked, stirring frequently. Drain; remove beef mixture from skillet.
In same skillet, combine gravy mix, pepper and water; mix well. Cook over medium-high heat for 3 to 5 minutes or until bubbly and thickened, stirring constantly. Remove from heat. Stir in sour cream and nutmeg.
Add cooked noodles and beef mixture to gravy; stir to combine. Spoon mixture into sprayed casserole; cover.
Bake at 375°F. for 30 to 40 minutes or until bubbly and thoroughly heated. Sprinkle with parsley.