Season both sides of the chicken with 1 teaspoon kosher salt and black pepper.

Set the Instant Pot to sauté. Heat 1/2 tablespoon of the olive oil. Once hot and shimmering, add half the chicken and sear both sides for 2 to 3 minutes each, just until brown (the chicken does not need to be cooked through). Do not disturb the chicken while each side sears.  Remove to a plate and set aside. Add the second half of the chicken and sear each side for 2 to 3 minutes each. Remove to the same plate.

With the Instant Pot still on sauté, add the remaining 1/2 tablespoon olive oil. Add the onion, garlic, chili powder, and remaining 1/2 teaspoon kosher salt. Let cook 3 minutes, until the onion beings to soften. Turn the Instant Pot off (on my model, I hit CANCEL). Stir in the chipotle peppers, tomatoes, and reserved chicken. Arrange the chicken pieces in a single layer (a little overlap is OK, and the chicken will be touching). Pour the lime juice over the top.

Lock the lid in place. Cook on manual pressure for 8 minutes. As soon as the time is up, vent immediately. Once you can open the lid, turn the Instant Pot off, and then remove the chicken to a large bowl or plate. Turn the Instant Pot to SAUTE. Bring the cooking liquid to a simmer. Let simmer for 5 to 10 minutes, stirring occasionally, until the liquid reduces by about half. Meanwhile, shred the chicken with two forks (or, once it is cool enough, your fingers).

Once the liquid is reduced, turn the Instant Pot off, return the chicken into the Instant Pot, and then stir the chicken to coat in the sauce.

Prepare the avocado sauce (I like to do this while the chicken is pressure cooking): In a food processor, blend together the avocado, Greek yogurt, 2 tablespoons lime juice, and salt until smooth. Taste and add additional salt or lime juice as desired.