Season the chicken breasts with salt and pepper on both sides.
Press “Saute” mode on the Instant Pot and add 1 tablespoon of oil. Once the oil is heated, add the seasoned chicken and sear it for 4-5 minutes (flipping halfway through) until slightly brown. Remove the chicken breasts to a plate and set them aside.
Add the remaining 1 tablespoon of oil to the Instant Pot and add the sliced onions. Saute for 3-5 minutes until the onions are softened. Stir in the diced tomatoes, salsa, and taco seasoning, and let that simmer for 2 minutes.
Transfer the chicken back to the Instant Pot along with any juices on the plate. Pour in the lime juice as well. Cancel the” saute” mode and close the lid. Turn the valve in the “Sealing” position and cook the chicken on high pressure/manual setting for 10 minutes.
Once the cycle is complete, let the pressure naturally release for 5 minutes, and then quick release the remaining pressure. Remove the chicken from the pot, shred the chicken with two forks, and then transfer it back to the Instant Pot.
Press the “Saute” button and allow the chicken to simmer for 4-5 minutes.
Add the chopped cilantro to the pot and “cancel” the Instant Pot. Transfer the shredded chicken to a bowl and set it aside. for now.
To prepare the avocado cilantro sauce, add the avocado, Greek yogurt, cilantro, lime juice, and a pinch of salt t o a food processor and blend until it has a smooth consistency. Set the sauce aside.
To assemble the tacos, warm the corn tortillas on stove burners over a low flame until just slightly charred, or cook them in a hot skillet. Fill the tortillas with about 1/4 cup of the shredded chicken, add sliced radishes and jalapenos as toppings, and then drizzle the avocado cilantro sauce over the tacos. Garnish with cilantro and serve while still warm.
Notes
There will be leftover chicken. It's great for burritos, rice bowls, quesadillas, and more!
Leftover chicken can be stored in an air-tight container in the fridge for up to 5 days.