Use a pressure cooker to cook together the dal, green mango slices with turmeric powder and salt with double the amount of water. If you are not using a cooker, simply boil the lentils in about 5 cups of water in a large saucepan till the lentils are soft and mushy.
Heat oil in a kadhai or large pot. Add the mustard seeds and dried red chillies. Once it pops, add the ginger and garlic pounded together. Saute for 30 secs then add the onion. Cook for 3-4 minutes till soft.
Now add the dal into the pot. Stir and cook on low flame for 5-6 mins. Garnish with chopped cilantro and mix.
Now heat a small tadka pan (tempering pan), add ghee. Splutter a little more mustard seeds, 10 curry leaves and a pinch of hing. Pour immediately over the dal and cover.
Let it rest for 5 mins before serving.