In a large skillet, brown beef in oil on all sides. Transfer meat to a 5-qt. slow cooker. Add onions and peppers. Combine tomatoes, water, garlic, cilantro, beef bouillon, pepper, cumin and oregano; pour over vegetables., Cover and cook on low for 6-8 hours or until meat is tender. Remove beef; cool slightly. Skim fat from cooking juices; stir in olives. Shred beef with two forks and return to slow cooker; heat through. Serve with rice if desired.