In a small bowl, combine the salt, black pepper, paprika, oregano leaves, and chili powder; reserve.
Place the frozen roast into the Instant Pot; pour the beef broth over the roast into the pot.
Sprinkle the prepared spice blend over the wet frozen roast.
Top the roast with the sliced onions and crushed garlic, allowing the excess to fall into the broth in the Instant Pot.
Lock the Instant Pot lid into place. Use the manual setting to choose High Pressure, setting the cook time for 75 minutes. bringing the Instant Pot to full pressure.
When the timer sounds, allow a natural pressure release for at least 30 minutes. If any pressure remains in the Instant Pot after the 30 minute natural release, perform a quick release to remove the pressure.
Carefully unlock and remove the Instant Pot lid. Use a fork to test the roast to be sure it is fully fork-tender. **If you meet any resistance when testing the roast at this point, lock the Instant Pot lid back into place and cook the roast for an additional 10 minutes, followed by a second natural release of 15-20 minutes.
Remove the cooked roast to a cutting board and use two forks to shred the meat into pieces. Serve at once, or cool the roast fully and store in an air tight container in the fridge for up to 3 days.