Wash the moong dal 2-3 times until the water runs clear. Soak for 20-30 minutes. See notes.
To a large pot add the soaked moong, ½ the salt and turmeric along-with 3 cups of water and place it on high heat until it comes to a rolling boil. See Notes for other cooking options.( If you are using a pressure cooker place it on medium.)
Once water starts to boil turn down the heat to medium low, cover with a lid and let it cook until the lentils are soft, about 15 minutes.
While the moong dal cooks make the tempering/ tadka. Heat oil/ghee in a medium sized saucepan, once warmed add cumin seeds. Once the seeds begin to sizzle and pop add the garlic, ginger, asafetida and curry leaves if using. Stir and allow to cook for a minute, be careful as it burns very quickly.
Add the green chillies if using and the chopped tomatoes and remaining salt. Stir and leave it to simmer on medium heat for 4-5 minutes. The moisture of the tomatoes should have reduced and the oil starts to separate from the tomatoes. At this point transfer the tempering to the cooked moong dal. Stir well and bring it back to a simmer. Stir in the dried fenugreek leaves if using.
Take it off the heat off. Stir in the chopped spinach, cover and allow the spinach to cook in the residual heat of the steaming dal. Enjoy!!