Heat the olive oil in a large pot over medium heat. Add the chopped onion and sauté for about 5 minutes, or until softened.
Stir in the minced garlic, chopped bell pepper, and carrots, and cook for another 3-4 minutes until the vegetables are tender.
Add the black beans, diced tomatoes (with juices), chicken broth, cumin, chili powder, salt, and black pepper. Stir well to combine.
Bring the mixture to a boil, then reduce the heat and simmer for about 15 minutes. Stir occasionally.
Add the shredded chicken and corn to the pot, and cook for an additional 5-10 minutes, allowing the chicken to heat through.
Just before serving, stir in the lime juice for added brightness.
Serve the soup hot in bowls, topped with tortilla strips, fresh cilantro, avocado slices, and a dollop of sour cream if desired.