Heat the oil, and add the cumin seeds, brown mustard seeds and guajillo pepper pieces. Cover and heat until the brown mustard seeds start to pop and spatter.
Add the green peppers and saute until the just start to soften, then add the potatoes and other spices and stir. Turn the flame down and cook until the potatoes are done (about 10-15 minutes depending on how finely they are chopped), stirring occasionally. If the mix gets too dry and starts to scorch, add just enough water to keep from burning.