Heat a large sized saucepan on high heat and add the water, garlic, lentils, onion, tomato, salt, turmeric, and cayenne pepper and bring to a boil, reduce to a simmer, place lid off center and cook for about an hour or until the mixture is thickened and the lentils are tender, stir often so no burnt spots. Remove from heat and set aside.
For the Tarka
In a small pan, heat the 1 1/2 teaspoons of oil, add the sliced onions and cook, stirring until the onions are golden brown, use a bit more oil if needed.
To serve, place some some curry in a serving bowl, top with some of tarka and cliantro.
Provided courtesy of good friend, Stephen Connell.