Combine the beef, cooked rice, onion, salt, chili powder, bread crumbs, and egg. Mix well. Shape into 1-inch meatballs; set aside.
Bring all the remaining ingredients except the cilantro to a boil in a large pot. Add the meatballs when the stock begins to boil. Cover and reduce the heat to a simmer. Cook for 20 minutes. Skim off any fat that rises. Turn the heat off. Add the chopped cilantro and serve.