1Mix cocoa powder and seasonings in small bowl. Set aside. Heat 1 tablespoon of the oil in large skillet on medium-high heat. Add 1/2 of the beef; brown on all sides. Remove beef from skillet. Repeat with remaining beef, adding additional 1 tablespoon oil as needed.
2Heat remaining 1 tablespoon oil in same skillet on medium heat. Add onion; cook and stir 3 minutes. Add water; stir to loosen browned bits in bottom of skillet.
3Stir in beef, beef stock, tomato paste and seasoning mixture. Bring to boil. Reduce heat to low. Simmer, uncovered, 1 1/2 hours or until beef is tender, stirring occasionally. Serve over cooked rice with shredded cheese and sliced green onions, if desired.