In a pressure cooker, add washed and drained dal. To this add chopped onion, tomato, green chilies, cumin seeds, chopped ginger, and chopped garlic. Add 3 cups of water along with 2 tablespoons of cooking oil and place the lid. Cook according to the timing of the pressure cooker, mine cooks in 20 to 25 minutes.
After releasing the pressure, open the lid safely, and with help of a whisk, blend the cooked dal till it gets thicker and creamy. Transfer the lentils to another vessel and add turmeric powder, salt, and lemon juice. Cook on low heat for 5 minutes or till it starts to boil.
In a small pan, heat cooking oil or ghee. When it is hot, add mustard seeds and cook for a minute or till it stops spluttering. Then add sliced garlic and cook till it slightly changes color. Now add the rest of the tadka ingredients and pour over the cooked dal. Garnish with ghee and chopped coriander leaves.
Serve hot with steamed rice.