In a large flat container or bowl, mix the oregano, chili powder, cumin, salt and pepper. Sprinkle all sides of the meat with the mixture and place in the instant pot.
Place the onion and chilis in the instant pot. Then place the garlic, cut side down, on the meat.
Pour the orange juice, lime juice, and coke over the meat.
Seal the instant pot and set the meat cycle for 90 minutes.
When the time has finished, let it slow release.
Open and place the meat on a cutting board or plate. Remove any pieces of fat and using two forks pull the meat apart.
Set the broiler for 500° and cover a cookie sheet in tin foil.
Place meat on the cookie sheet. Spoon some of the broth over the meat. Place under the broiler till crispy, about 5 minutes. Stir the meat and crisp again.
Remove meat from the oven and serve.