Heat a heavy skillet over high heat, add the oil, and when hot, reduce the heat to medium, add the pork, and brown. Remove the pork when it is browned, and add it to the posole. Add the onions to the skillet, and fi needed, additional oil. Add the onions to the skillet, and if needed, additional oil. Saute the onions until they turn a golden brown, 5 to 10 minutes. Add the garlic and cook for an additional minute. Transfer the mixture to the pot with the posole.
