Pick over, wash and drain the split mung beans. Place the beans, water, turmeric, coriander, ginger root, and a little dab of the oil/ghee in a heavy 3-quart saucepan. Stirring occasionally, bring to a full boil over high heat. Reduce heat to moderately low, cover with a tight-fitting lid and boil gently for an hour or so, or until dal is soft and fully cooked.

Remove from heat, uncover, and add salt. Beat with a wire whisk until the dal soup is creamy smooth. Add the spinach, cover and boil gently once more for 5-8 minutes if using fresh, or 2-3 minutes if using frozen.

Heat the ghee or oil in a small saucepan over moderate to moderately high heat. When it is hot, pour in the cumin seeds and fry until they're brown. Add the asafetida and cayenne and fry for just 1-2 seconds more. Then quickly pour the fried seasonings into the soup. Cover immediately. Let the seasonings soak into the hot dal for 1-2 minutes. Stir in the lemon juice and serve.