In a dutch oven combine tomatoes, undrained kidney beans, drained garbonzo and pinto beans, tomato paste, undrained chili peppers, onions, zucchini, chili powder, cumin, garlic powder, sugar, salt to taste, if desired. Heat to boiling; reduce heat. Simmer, covered, 30 minutes. Remove from heat. Add cheese; stir till melted.
Serve with sour cream and garnish with cilantro, if desired.