Dice the onion into 1/2-inch pieces, mince the garlic cloves, finely chop the chipotle peppers, and juice the limes to get 1/4 cup plus 2 tablespoons. Cut the chicken breasts into 2-inch chunks—this smaller size will cook faster and more evenly in the Instant Pot compared to whole breasts. Season all the chicken pieces generously with kosher salt and ground black pepper, tossing to coat evenly. I like to season the chicken right before searing so the salt doesn't start breaking down the proteins prematurely.

Set the Instant Pot to sauté mode and add the olive oil, allowing it to heat until shimmering. Working in two batches to avoid overcrowding the pot, sear the seasoned chicken for 2-3 minutes per side until golden brown on the exterior. This browning step (called the Maillard reaction) develops deep, savory flavors that make the final dish taste richer. Don't worry about cooking the chicken through—it will finish cooking under pressure. Remove each batch to a bowl as it's done.

Add the diced onion, minced garlic, chili powder, and 0.25 teaspoon kosher salt to the pot (there should still be flavorful browned bits on the bottom). Sauté for about 3 minutes, stirring occasionally, until the onion begins to soften and the chili powder becomes fragrant. This blooming of the spices releases their essential oils and deepens their flavor throughout the entire dish.

Turn off the sauté function. Stir in the finely chopped chipotle peppers and the canned diced tomatoes (with their juice), then add the seared chicken back to the pot along with the 0.25 cup of fresh lime juice. Stir everything together to combine. Lock the Instant Pot lid and set it to high pressure for 8 minutes. Once the cooking time is complete, carefully quick-release the pressure by turning the vent valve to venting immediately—this stops the cooking process and prevents the chicken from becoming dry.

Using a slotted spoon or tongs, carefully remove the cooked chicken pieces to a bowl. Switch the pot back to sauté mode and let the cooking liquid simmer for 5-10 minutes, stirring occasionally, until the sauce reduces by about half and becomes more concentrated and flavorful. While the sauce reduces, shred the chicken into bite-sized pieces using two forks or your hands (it should shred easily since it's fully cooked). I find this is the perfect time to do the shredding while the sauce concentrates—it saves you a step and keeps your workflow moving.

Turn off the sauté function. Return the shredded chicken from Step 5 to the pot with the reduced sauce and stir until the chicken is evenly coated. Let it sit for a minute to allow the flavors to meld.

While the chicken finishes, blend the halved and pitted avocado, nonfat Greek yogurt, 2 tablespoons fresh lime juice, and 0.25 teaspoon kosher salt in a blender or food processor until smooth and creamy. Warm your tortillas or taco shells. Fill each shell with the seasoned chicken mixture, drizzle generously with the creamy avocado sauce, and top with fresh cilantro if desired. The yogurt keeps the sauce lighter than traditional guacamole while adding a tangy richness that complements the smoky chipotle chicken beautifully.