Heat the oil in a large heavy-based pan over a medium heat.
Add the onion and fry until it is lightly browned,stirring so it doesn't stick and burn.
Add the garlic and cook for 2 minutes.
Add the turmeric and paprika and cook for a moment.
Add the tomatoes and ginger and cook for a further 5 minutes.
Add the tamarind water and the reserved lentil liquid.
Simmer the mixture,covered,over a low heat for 15-20 minutes.
Add the lentils,garam masala and cumin and cook for about 3 minutes or until the lentils are heated through.
Check seasoning,place in a bowl and sprinkle with shallots.
Serve with steamed rice or a rice pilaf.
Tamarind water
Soak 1 cup tamarind pulp in 1 1/2 cups boiling water for 20 minutes,then strain it.
Serves 4