Add chicken broth to Instant Pot.
Place metal grill piece (came with Instant Pot) on the bottom of your pot and place chicken on the grill in a single layer.
Empty half of the seasoning packet onto the chicken.
Place lid on the Instant Pot and set the seal. Press the "Poultry" button and let the pressure cooker work its magic. I used defrosted chicken so after the standard 20 minute poultry cook time, my chicken was cooked thoroughly.
When the timer goes off (indicating the end of the cook time), release the pressure slowly and remove the lid.
Remove the chicken and shred it. You can shred it manually with a fork or toss it into a food processor. I used my food processor and shredded all of the chicken.
Press "cancel" on your Instant Pot to turn off the pressure cooker mode. Leave the taco seasoned chicken broth in the pot and add the raw onions and green peppers.
Add the shredded chicken and the remaining half packet of taco seasoning.
Stir until just combined. Replace the Instant Pot lid and select "Slow Cooker" mode. Choose how long you'd like it to slow cook. I made the chicken in the early afternoon hours and we were eating this for dinner that same night. I selected 4 hours on the slow cooker mode to keep it cooked and warm until dinnertime.
A few minutes before you are ready to eat, drain the fajita mixture and place it in a bowl.
We served the meat with typical taco fixins' on the side (lettuce, shredded cheese, diced tomatoes) and also put out hard taco shells and soft tortilla shells.