In a large skillet, cook the beef, onion and green pepper until meat is no longer pink; drain. Add the next 8 ingredients; bring to a boil. Reduce heat; cover and simmer for 10 minutes. Combine cheeses. , In a 5-qt. slow cooker, layer about 3/4 cup beef mixture, 1 tortilla and about 1/3 cup cheese. Repeat layers. Cover and cook on low for 5-7 hours or until heated through. If desired, serve with optional toppings.