In a gallon-sized resealable bag, add chicken, garlic, lemon juice, onion, olive oil, red wine vinegar, oregano, allspice, and lemon pepper.
Mix well so that all the chicken is covered in marinade.
Let marinate in fridge for at least 2-3 hours (6-8 is ideal for best flavor).
When chicken is finished marinating, pour 1 cup of chicken broth into the bottom of the Instant Pot.
Dump the entire contents of the bag (chicken and marinade) into the Instant Pot.
Place lid on pot and press MANUAL (or PRESSURE COOK) and set timer for 10 minutes.
Allow 10-15 minutes to come to pressure before it starts the countdown cook timer.
Once it is finished cooking, do a natural release of the pressure for 5-10 minutes and then a quick release of the remaining pressure. Remove the lid.
Shred cooked chicken using 2 forks.