Heat oil in the pressure cooker on saute setting
Cut the skirt steak into pieces small enough to fit in the pressure cooker and season on one side with salt and pepper.
Brown each piece of skirt steak and set aside.
Once all the meat has been browned, cook the onions and peppers in the instant pot, using the liquid they express to scrape up the bits of beef fond from browning the meat
Add the garlic toward the end of cooking the onions
Add the cumin, diced tomatoes, and Worcestershire sauce and cook for a few more minutes
Add the tomato paste and stir into the onions. Add about a cup of the beef stock and stir to combine.
Return the steak along with any juices that have collected underneath it to the pot. Pour in enough beef stock to cover.
Pressure cook on the Meat setting for 45 minutes then allow the steam to dissipate
Using a spider (the meat will be very tender at this point and will fall apart if you grab it with tongs), remove the meat to a bowl to be shredded. Leaving the pressure cooker unlidded but with the heat on, allow the liquid to reduce while shredding the beef.
Shred the beef using two forks
Return the shredded beef to to the cooking liquid. Add the parsley and cilantro and stir to combine. Allow to come up to temperature and then serve