Rinse the yellow moong dal under cold water until the water runs clear.
In a saucepan, add 3 cups of water and the rinsed moong dal.
Bring to a boil over medium-high heat.
Reduce the heat to low and let the lentils simmer until they are tender, stirring occasionally, for about 20 minutes.
In another pan, heat oil over medium heat.
Add the cumin seeds and fry them for about a minute until they become aromatic.
Add the chopped onion, minced ginger, minced garlic, and one sliced tomato to the pan.
Cook, stirring constantly, for about 10 minutes on medium-low heat until the onions are softened and translucent.
Once the lentils are cooked, add them to the pan along with turmeric powder and 3 cups of water.
Bring the mixture to a boil.
Let it simmer for a few minutes until the flavors are well combined and the dal reaches the desired consistency.
Season with salt to taste, and then turn off the heat.
Garnish with the remaining sliced tomato and chopped coriander/cilantro leaves immediately after turning off the heat.