Start by heating the olive oil in a large pot over medium heat. Add the diced onion and cook it for about 3–4 minutes until it softens and becomes translucent. Stir in the minced garlic and let it cook for another 30 seconds until fragrant. This forms the flavor base of your soup.
Add your chicken breasts or thighs into the pot, then sprinkle in the taco seasoning, chili powder (if using), and ground cumin. Stir everything well so the chicken gets coated with all those bold spices. Let it sear for a minute or two to lock in flavor before adding liquids.
Now pour in the black beans, kidney beans, corn, both kinds of diced tomatoes, and chicken broth. Stir everything together until well combined. Make sure the chicken is mostly submerged in the broth so it cooks evenly. Bring the mixture to a boil.
Once it boils, reduce the heat to low and cover the pot. Let the soup simmer for 20–25 minutes. This gives the chicken time to cook through and lets the flavors come together. After that, remove the chicken and shred it using two forks.
Add the shredded chicken back into the pot and stir well. Add a tablespoon of lime juice for brightness, and season with salt and pepper to your taste. Give the soup a few more minutes on low heat so the chicken can absorb some of the flavor.
Ladle the soup into bowls and top with your favorite garnishes. A handful of shredded cheese, a dollop of sour cream, creamy avocado slices, and a sprinkle of cilantro make it extra delicious. Finish with crushed tortilla chips and a wedge of lime for a satisfying, hearty bowl.