Step 1

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

Step 2

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.

Step 3

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.

Step 4

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).

Step 5

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.

Step 6

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.

Step 7

To serve: Fill the shells with the chicken, drizzle with avocado sauce, and add any desired toppings. Enjoy immediately.