Peel and cube potatoes. Heat oil in pan and stir in mustard seed. Stir until the crackle. Add cumin, turmeric, coriander, cayenne, ginger, red and green chiles. Cook for 30 seconds. Add potatoes and fry for 3 minutes. Meanwhile heat oil in pan, add ginger, red and green chiles. Stir for 20 seconds. Add cilantro and mix well. Sprinkle with lime juice. Spoon potatoes into serving dish and pour lime juice mixture over the top. Serve with rice.