Season the chicken breasts with salt and pepper. Heat olive oil in a large pot over medium-high heat, and cook the chicken until golden brown on both sides, about 6-8 minutes per side. Remove and set aside.

In the same pot, add diced onion and cook until translucent. Stir in garlic, cumin, and chili powder, and cook for another minute. Add chicken broth, tomatoes, black beans, and corn. Bring to a simmer and cook for 20 minutes.

Once the chicken is cool enough to handle, shred it using two forks and add it back to the pot. Let it warm through for about 5 minutes.

While the soup is cooking, heat vegetable oil in a pan over medium heat. Fry tortilla strips until crispy and golden. Drain on paper towels and season with salt.

Ladle the soup into bowls and top with crispy tortilla strips. Garnish with chopped cilantro, diced avocado, and a squeeze of lime juice if desired.

Store any leftover soup in an airtight container in the refrigerator for up to 3 days. Reheat gently on the stove before serving.