Pour one cup of water into the bottom of the Instant Pot, then arrange the chicken breasts directly in the water. Season with the salt, onion powder, garlic powder, and several grinds of black pepper over the top of the chicken.
Secure the lid and move the steam release valve to Sealing. Use the Manual or Pressure cook button to cook at high pressure for 10 minutes, if using chicken breasts that are 4 to 7 ounces in size. (For 8 to 12 oz. breasts, cook for 12 minutes, and for 13 to 16 oz. breasts, cook for 15 minutes.)
When the cooking cycle is complete, let the pressure naturally release for 10 minutes, then move the steam release valve to Venting to release any remaining pressure. When the floating valve in the lid drops, signaling that the pressure is gone, it's safe to open the lid.
Use a meat thermometer to make sure the internal temperature of the chicken has reached at least 165ºF. (In my experiments, it was never under, but you can always close the lid and let the chicken rest 5 more minutes, if needed.)
Use a hand mixer to shred the chicken breasts. It’s so quick and easy! (There's no need to drain the liquid in the pot first; I like to store the shredded chicken in the extra moisture.) If you don't have a hand mixer, transfer the chicken to a cutting board and use two forks to shred it, instead.
Serve the chicken right away, or store it in the fridge for up to 3 days to use over salads or add to stir-fries.
To cook frozen chicken breasts, make sure the individual breasts are not stuck frozen together for even cooking. I like to cook frozen chicken for 20 minutes at high pressure, but if the chicken breasts are particularly small (under 8 oz.) 15 minutes of cooking is usually sufficient.