Place the chicken in a slow cooker. Add the onion, black beans, corn, tomato sauce, diced tomatoes, green chilies, taco seasoning, and chicken broth, and stir to combine. Cover and cook on high heat for 4 hours or on low heat for 8 hours.Remove the chicken and shred. Return the shredded chicken to the slow cooker and mix well.To serve, ladle the soup into bowls. Garnish each serving with 2 tablespoons of tortilla strips.