Place sliced red onion in a strainer and boil a kettle of water.
In the jar you're using to store the pickled onion, place vinegar, salt, honey, garlic, and peppercorns. Stir until salt and honey are dissolved.
Once water boils, slowly pour water over the sliced onion. Blanching them so their slightly tender.
Give the strainer a little shake to help get rid of excessive water, then add onion to the jar with vinegar mixture. Press into jar until onion is fully submerged. Seal and place in refrigerator for AT LEAST 2 hours before using.
In an Instant Pot, pour half the jar of salsa and make sure bottom is evenly coated.
Place chicken on top of salsa, then onion on top of chicken.
In a small bowl, combine spices (salt through coriander). Season onion and chicken evenly, then top with remaining salsa.
Seal Instant Pot, then select "Meat/Stew" setting and cook for 90 minutes. Once it's done, let rest for 5 minutes, then release the vent for the steam.
After the steam settles, remove lid and, using two forks, shred the chicken!
Serve on tortillas with pickled onions and other toppings! You'll find some of our topping favorites listed above but we encourage you to add whatever your favorite toppings are!