Wash the yellow moong dal 2–3 times in water until the water runs mostly clear. Drain.
In a saucepan or pressure cooker, add the rinsed dal and 2 cups of water.
Cook for 1–2 whistles on medium heat.
Simmer uncovered for 15–20 minutes, or until the dal is soft and mushy. Stir occasionally and add more water if needed.
Once cooked, mash the dal slightly with the back of a spoon or ladle to make it creamy. Set aside.
In a small frying pan, heat 1 tablespoon of ghee or oil. Add cumin seeds and let them splutter. Add dried red chilies (if using), grated ginger, and chopped onion (if using). Sauté until onions turn golden.
Add chopped tomatoes and turmeric powder. Cook until the tomatoes soften.
Pour the tadka over the cooked dal. Add salt to taste. Mix well and simmer for 2–3 minutes to blend the flavors.
Garnish with fresh coriander leaves and a squeeze of lemon juice if desired. Serve hot with rice or roti.