Ingredients:
1 large Tomato
Small Piece of Ginger
1 Green Chilly
Pinch of Turmeric
3/4 cup cooked yellow lentils/Thogaribele/Toor dal
1-2 tsp Lemon Juice
3-4 Coriander Leaves
Salt to taste
1/4 tsp Mustard seeds
Pinch of Asafotida powder/Hingu
1 tsp Oil
Recipe:
Chop tomato into longer thin pieces as shown in the picture below. Smash ginger and cut the chilly into 2 pieces.

Add chopped tomato, ginger, chilly, salt, turmeric powder, water in a vessel and cook it well. Once tomato is cooked properly, add cooked yellow lentils and bring it to boil. (You can cook yellow lentils(3-4 whistles in a cooker) and keep it in fridge, it won't be spoilt for 10 days.) Add lemon juice and stir it. Keep the saaru in low flame for about 2-3 mins and stir it properly. Add chopped Coriander leaves and stir it.
Add mustard seeds and oil in a pan. Once it starts spluttering, add asafotida powder, keep it for few seconds and then add it to Saaru. Mix well before serving. It goes well with ghee, rice and papad.