Heat the oil in a pan and add mustard seeds. When it starts to pop add cumin seeds. Fry for few seconds and add urad dhal. Fry until brown. Then put in the potato cubes and fry for 2 minutes. Add chili powder, turmeric powder, garam masala & salt. Mix well. After couple of minutes sprinkle little water. Cover the pan. Lower the heat and cook until the potatoes are browned & fully cooked. Garnish with chopped coriander leaves.