First grind ginger , coriander and green chiilies to a paste. Heat oil in a cooker , add mustard seeds and then the chopped cabbage and potato. fry for 5 mins in low flame . then add the grinded masala and salt. Keep the cooker for one whistle and put off the flame. After a few mins , open the cooker , mash the potatoes and serve hot with roti or chapatti.