Heat oil over medium heat. When hot, add cumin seeds & let sizzle for a few seconds. Add the garlic & stir-fry till the garlic changes colour. Put in the onion & stir-fry until they begin to brown at the edges. Add the lentils & water. Bring to a boil, cover & simmer for about an hour, or until the lentils are tender. Add salt & cayenne. Stir to mix & cook another 5 minutes.