Spray 3 1/2- to 4-quart slow cooker with cooking spray. Mix chicken, sweet potatoes, onion, tomatoes, broth, oregano and cumin in cooker. Cover; cook on Low heat setting 7 to 8 hours.
Stir in corn and bell pepper. Increase heat setting to High; cover and cook about 30 minutes or until chicken is no longer pink in center and vegetables are tender.
Meanwhile, heat oven to 450°F. Spray 2 cookie sheets with cooking spray. Cut each tortilla into strips; place in single layer on cookie sheets. Bake about 6 minutes or until crisp but not brown; cool.
Spoon soup into individual bowls. Top with tortilla strips. Sprinkle with cilantro.