In the Instant Pot, pressure cooker or regular pot, combine the ribs, oregano, pepper, salt, garlic, and onion.Add enough water to come to the same level as the ribs.
2. Boiling
In Instant Pot: Close the lid and set the valve to SEALING. Set to HIGH PRESSURE and the timer to 30 minutes. When the cycle finishes, set the valve to VENTING. Once the pressure is released, carefully open it, and check that the meat is very tender. If needed, repeat this but set the timer to 10 minutes.In pressure cooker: Close the lid and place the valve. Boil for 30 minutes, turn off the heat, and 5 minutes later, carefully remove the valve to release pressure. Once the pressure is released, carefully open it, and check that the meat is very tender. If needed, repeat the process above, but boil for just 10 more minutes.In regular pot: Close the lid and place the pot on the stove. Boil over medium heat for about an hour, turning the ribs, and checking that it has enough liquid every ten minutes or so. Check that the meat is very tender. If needed, keep boiling, turning, and adding liquid as necessary until the meat is tender.
3. Removing from the liquid
Remove the ribs from the liquid onto a tray, tapping lightly to leave behind as much liquid as possible.Don't discard the liquid; freeze it to use as broth in soup another day.
4. Grilling
Cook at the maximum temperature on both sides for 3-5 minutes, or until they have a nice golden-brown color.I had to use a BBQ liner to be sure the ribs would not fall through the grill grate, but it's not absolutely necessary.