In a Dutch oven, cook beef, onion and peppers over medium-high heat until beef is no longer pink and vegetables are tender, breaking up beef into crumbles, 8-10 minutes; drain. Transfer to a 7-qt. slow cooker. Stir in tomatoes, beans, chili powder and cumin. Cook, covered, on low until flavors are blended, 5-6 hours., Meanwhile, cook macaroni according to package directions; drain. Add to slow cooker. Stir in cheese until melted. If desired, serve with sour cream and additional cheese.