Heat oil in skillet over moderate heat. Add cumin and stir for 2 seconds. Add turmeric and cook for 2 seconds. Add potatoes and toss to coat with spices. Add two tablespoons of water. Cover and reduce to low. Cook for 10 minutes. Add green onions, salt, cayenne and coriander. Stir well. Add more water if necessary. Cover, increase to medium. Continue cooking, for 5 minutes. Add lime juice and serve.