In a casserole cook the onions, peppers and garlic in the oil over moderate heat, stirring occasionally, for 5 minutes. Add the chili powder, cumin and oregano and cook, stirring, for 3 minutes. Add the tomato paste and cook, stirring, for 2 minutes more. Add the beef and cook, stirring occasionally, until no longer pink. Add the tomatoes, 1 cup of the broth, the vinegar and chocolate and bring the mixture to a boil, crushing the tomatoes with the back of a spoon. Simmer the chili, covered, for 1 hour, adding additional broth, if necessary. Add the kidney beans and simmer, uncovered, for 15 minutes more. Ladle into bowls and serve with rice and desired toppings.