Peel, quarter, and soak the potatoes in cold water. Meanwhile, heat the oil in a medium frying pan and saut, the onions until soft. Add the garlic and stir in the drained potatoes, stirring over medium heat for a minute. Pour in the tomatoes and enough water to almost cover the potatoes, if necessary. Sprinkle in the parsley and season with salt and pepper. Cover and simmer over low heat for 30 minutes, then uncover and continue cooking over low heat until the potatoes are tender and the sauce is thick, turning the potatoes occasionally. Transfer to a warm bowl and serve warm.
