Mix together all the spices.
Trim the pork so you still have some fat, fat is flavor after all. You want at least 10%. Cut the pork into 1 1/2 lb pieces and dust with spice mix. Rub it in good. Pat it, slap it. Make sure you get it into all nooks and crannies.
Place in plastic bag and store in refrigerator for at least 2 hours up to over night.
When ready to cook, in your pressure cooker add the vegetable oil and bring to shimmer. Add pork and brown off all sides. Add 3 cups of water or just enough to come half way up the pork. Add diced onions. Bring up to a boil and seal the pressure cooker. When it starts to spit on high pressure reduce heat just enough to maintain the hiss.
Cook for 1 hour on high pressure. Remove from heat and allow to depressurize naturally. In other words just let it cool down. This is important. Don't be in a hurry.
Take out the pork with a slotted spoon. It will just fall apart so do not try a fork or other implement of destruction. Make sure you get some of the onions mixed in with the pork.
With two forks pull the pork apart, hence pulled pork. Now it is up to you what to do with it but I will bet you will not be able to resist mixing a little bit together with a good BBQ sauce and making a sandwich. Betcha.
If you want you can add a couple of tablespoons of unsweetened cocoa to make this really authentic.