Set the Instant Pot to sauté mode. Add the diced onion and minced garlic. Cook for 2 minutes until the onion softens.
Stir in the cumin, chili powder, and salt. Cook for 30 seconds until the spices smell fragrant.
Add the chicken breasts, chicken broth, diced tomatoes, black beans, and frozen corn. Stir once to combine.
Secure the lid and set the valve to sealing. Cook on manual high pressure for 10 minutes.
Allow a natural pressure release for 10 minutes, then quick release any remaining pressure.
Remove the chicken breasts and shred them with two forks. Return the shredded chicken to the pot.
Stir in the lime juice. Ladle the soup into bowls and add tortilla strips, cilantro, and avocado right before serving.