Soak moong in enough water overnight or for at least one hour.
Add soaked moong into a pressure cooker with one cup water, half the quantity of the measured turmeric powder and half of the cumin seeds.
Allow moong to cook for 3 whistles over medium heat. If you don't have a pressure cooker, cook them in a pan over medium heat till done.
Allow the pressure cooker to cool down before you open the lid.
Add oil or ghee in a deep saucepan. Place the pan over medium heat.
When the oil or ghee becomes hot, add mustard seeds, followed by the remaining cumin seeds.
Add curry leaves and chopped onion. Stir fry till the onion becomes soft and begins to brown a little.
Add ginger, garlic and chillis and stir fry for a few seconds.
Add remaining turmeric powder.
Immediately add tomato puree. Add salt and coriander cumin powder.
Allow the tomato puree to cook for 2-3 minutes.
Add the cooked moong along with the water. Add the remaining water.
Mix well, lower the heat and allow the moong curry to simmer for 10-15 minutes.
Add chopped fresh coriander and lemon juice just before serving.Serve with some plain rice, roti or paratha.