Wash the moong dal thoroughly, then soak the moong dal for 20 minutes.
While it is soaking, cut the onion, grate the ginger and 1 tomato. Heat 1 tbsp of ghee or oil in a saucepan (pot), then add the onion and ginger and fry for 5 minutes, then add the grated tomato, and continue cooking for 5 minutes longer over medium heat.
Stir in the moong dal, turmeric and a 1 tsp of salt and stir to combine, then pour in the water, turn the heat up and bring to a boil, then lower the heat and simmer until tender for 20 minutes.
When the dal is close to being done, start on the tadka. In a small saucepan heat the ghee, then add the asafetida and cumin seeds. They will start to pop and sizzle, add thinly sliced onions, cook them until they turn crispy on medium high heat, then add sliced garlic and the chilli powder and cook for a few seconds until the garlic is only slightly browned. Then take off the heat and pour all over the moong dal. Cover with the lid and let it infuse for about 5 minutes.