Rinse the mung dal lentils under water until the water runs clear. Add them to a pot along with 1200ml of water, 1 tsp turmeric and 1 tsp asafoetida. Boil for 30-40 minutes or until the lentils are fully cooked and have formed a stew.
Heat 4 - 6 tbsp of vegetable oil in a pan, add the chopped red onion and sauté until starting to soften. Scoop the red onion to one side of the pan and on the other side add 2 tsp cumin seeds. Fry them until they start to sizzle. Then add the minced ginger, pressed garlic, dried curry leaves and mix everything together.
Add the chopped tomatoes to the pan and allow to simmer until the tomatoes have fully cooked about 10 minutes.
Before plating, add the Kasuri methi and garam masala to the lentils and give them a good stir. Allow to sit for about 5 minutes and then pour lentils onto a dish, scoop some tadka over and serve with rice or flatbreads.