Cook thuvar dhall with turmeric, with 2 cups of water. Add chopped tomatoes, green chilles, ginger, hing, and salt, to this and let this cook for 5-10 minutes. Heat some ghee, splutter mustard, then add cumin seeds, red chillies, and curry leaves, and add cumin powder, and pepper powder before mixing this to the boiling rasam. Squeeze lemon juice and garnish with chopped cilantro.