Combine diced onion, garlic, half the cilantro, chicken breast (whole or diced), broth, tomatoes, and all spices in Instant Pot.
Close the lid, set valve to sealing, and program for soup.
At the end of cook time, quick release the pressure.
Remove and shred or chop chicken breasts (if cooked whole).
Add chicken back to the soup along with 1 cup of cheese, and half of the tortilla strips (crushed). Stir well. If too much broth/liquid has evaporated and you would like it to be thinner, you can add some water at this point (or more broth).
Spoon soup into 4 bowls. Top with remaining tortilla strips, shredded cheese, avocado chunks, and chopped cilantro, if desired.