Wash lentils. Bring plenty of water (six cups) with turmeric to a boil in a large saucepan and cook lentils until overdone and mushy, approximately 15 minutes.
In a different saucepan, heat oil on medium heat. Add mustard seeds and curry leaves until seeds start to pop (no more than 30 seconds). Add tomatoes and fry for about three minutes. Add onions, garlic, methi leaves, curry powder, salt, chili powder and sugar. Add mashed lentils and boil for five minutes. Add one cup of water to dilute to curry consistency.
Remove from heat and add garam masala. Sprinkle with chopped cilantro before serving. Serve with chapatis, roti or rice.