Cook ground chuck and onion in large skillet over medium heat,stirring til beef crumbles and is no longer pink. Drain and return to skillet.
Add barbecue sauce and next 4 ingredients to beef mixture. Bring to a boil; cover, reduce heat and simmer 10 minutes, stirring once.
Mix cream cheese and sour cream, stirring til smooth. Stir in green onions and cooked noodles.
Layer half of noodle mixture in greased 13 x 9 inch baking dish. Top with half of beef mixture. Sprinkle with 1 cup cheese. Top with remaining noodle mixture and remaining beef mixture. If desired, cover and chill overnight. Let stand at room temperature 30 minutes before baking.
Cover and bake at 350 for 30 minutes or til thoroughly heated. Uncover and sprinkle with remaining 1 1/2 cups cheese; bake 5 more minutes. Garnish if desired. Makes 8 servings.