In a large saucepan, cook the beef, onions and garlic until meat is no longer pink, 5-7 minutes; crumble meat; drain. Stir in the tomatoes, chiles and pepper; bring to a boil. , Reduce heat; simmer, uncovered, for 10-15 minutes. Stir in cheese until melted. Serve immediately. If desired, top with sour cream, jalapenos, tomatoes and cilantro.