If desired, heat the olive oil in a skillet over medium heat. Sauté the chopped onion and minced garlic for about 2-3 minutes until softened, then transfer to the slow cooker.
Place the chicken breasts in the slow cooker. Add the black beans, corn, diced tomatoes, chicken broth, chili powder, cumin, paprika, oregano, salt, and pepper. Stir gently to combine all the ingredients.
Set the slow cooker on low for 6 hours or high for 3 hours, until the chicken is cooked through and easily shredded.
About 15 minutes before serving, shred the chicken directly in the slow cooker using two forks, then give everything a good stir.
To serve, ladle the soup into bowls and top with crispy tortilla strips, fresh cilantro, and a squeeze of lime if desired.
For a spicier version, add jalapeños or a dash of hot sauce to the mix.
You can top the soup with avocado, cheese, or sour cream for added richness.
Leftover soup can be stored in an airtight container in the refrigerator for up to 3 days.