In a measuring cup, combine the cola, Worcestershire sauce, garlic, vinegar, bouillon and seasonings; set aside. Cut roast in half. In a nonstick skillet, brown meat in oil on all sides.

Place onions in a 3-qt. slow cooker. Top with meat. Pour half of cola mixture over meat. Cover and cook on low for 8-10 hours or until meat is tender. Cover and refrigerate remaining cola mixture.

Remove meat from cooking liquid and cool. Strain cooking liquid, reserving onions and discarding the liquid. When meat is cool enough to handle, shred with two forks. Return meat and onions to slow cooker.