Stir in chili powder, bay leaves, cocoa powder, salt and cinnamon. Add tomatoes with their juices, breaking up with back of spoon. Mix in stock and tomato sauce. Bring to boil. Reduce heat; simmer 45 minutes, stirring occasionally.
Add beans to chili and simmer until flavors blend, about 10 minutes longer. Discard bay leaves. (Can be prepared 1 day ahead. Cover and refrigerate. Rewarm over medium-low heat before continuing.)
Ladle chili into bowls. Pass red onion, cilantro and yogurt separately.