Cook the onions and jalapenos in the vegetable oil in a large saucepan over medium heat until soft, about 5 minutes. Add the cumin, oregano, salt and garlic, and cook another 2 to 3 minutes. Add the beans, stock and 1 cup water and bring to a boil. Turn the heat to low and simmer 15 minutes.
Remove the beans from the heat and strain, reserving the liquid. Mash the beans in a small bowl with a potato masher, adding the vinegar and cooking liquid to keep the beans soft. (You will probably not use all the liquid.).
Recipe courtesy of Melissa d'Arabian