Heat the oil in a heavy large skillet over medium-high heat. Add the chorizo and cook, breaking up the clumps, until dry and crisp, about ten minutes. Using a slotted spoon, transfer the chorizo to a paper lined plate to absorb any additional oil. Pour off all but one tablespoon of fat from the pan and heat the pan over medium-high heat. Add the onions and boiled potatoes and saute until brown, about 12 minutes. Stir in the cooked chorizo and season with just a little salt and pepper, to taste. Transfer to a serving bowl and serve.
Notes: Mexican chorizo is an uncooked sausage, made with fresh ground pork and well seasoned with smoked red chiles. Since it's fresh, you will need to remove the casing before cooking it. They can be found at most supermarkets. Also, some chorizos are very salty so watch the seasoning!
A great filling for soft tacos, just add shredded cheese, beans or your favorite taco filling!