Place the stainless steel inner pot inside the Instant Pot® and add the water, chicken, and salt. Close and lock the Instant Pot® lid, making sure the steam release handle is turned to Sealing. Press Soup/Broth and set time to 8 Minutes.
When the time is up, release the steam (by turning the handle). Once all the pressure has been released, open the lid, remove the chicken, shred, and set aside.
For the mayonnaise, blend the egg on the lowest speed, add the oil in a steady stream, and add the rest of the ingredients. Set aside.
For the filling, mix all the ingredients together. Set aside.
Cut the avocados in half and bathe in lemon to avoid browning.
Place the avocados on a plate, stuff with the filling, and garnish with lemon slices.