1. Wash and pressure cook dal until very soft. Add tamarind, half tomato and 1 chopped onion to the dal.
2. Chop the remaining onions and tomato to medium or fine pieces. Heat oil and add mustard seeds, curry leaves and allow to splutter. Add onion, pumpkin, tomato and stir fry for 2 minutes. Add dal and bring to a boil on high. Add enough water to get sambar consistency. Simmer for 12-15 minutes on low fire, till it releases a flavour.
3. Add chopped coriander leaves before serving. Serve hot.