In a large non-stick pot, heat the oil on medium heat.
Tear the curry leaves in half and add it to the pot, along with the black mustard seeds and asafetida. Fry for a few seconds until fragrant.
Immediately add the garlic and ginger. Fry for a few seconds. Add the onions and green jalapeno chili. Saute until fragrant and the onions start to become translucent. Be sure not to burn the mixture. If you find this happening, either add some more oil or turn down the heat.
Add the cooked black lentils, 1 cup water, turmeric powder, and salt. Combine and bring the soup to a gentle simmer. Turn down the heat to medium-low to maintain a gentle simmer.
Add the chopped tomato, ground cumin powder, lemon juice, and jaggery.
Continue to simmer on low heat. uncovered, until some of the water boils off and the soup becomes thick in consistency (about 10-20 min), mixing occasionally. If you start to feel the soup becoming too thick, you can add a little more water.
Add the chopped cilantro. If needed, season once more with salt, lemon juice, and/or jaggery to taste. Simmer for additional 3-5 minutes.
Garnish with some fresh cilantro and serve warm with some fresh roti, naan, or toasted french bread.
Notes
To Cook Black Lentils - Add the black lentils in a bowl. Wash and soak in water for about 20-30 minutes. Drain the water and cook using one of two methods: (1) Pressure Cooker , or (2) Pot of boiling water. Cook the Dal until soft, but not mushy. Drain the water after cooking the dal.I typically cook a bunch at once in my pressure cooker, cool, and freeze leftover plain cooked black lentils in a freezer bag. Then simply thaw and use to make this soup for a quick meal when needed.Asafetida (hing)- Although this powder is naturally gluten-free, it is almost always manufactured by diluting it significantly with wheat flour. There are some brands you can find that make it with rice flour. If you are uncertain and have a gluten-free diet, then you can easily omit this ingredient.