In a saucepan, combine the lentils with the turmeric and 1.2l of water; bring to a boil. Cover partially and simmer over low heat for 20 minutes, until the lentils are barely tender.
In a small frying pan, heat the oil until shimmering. Add the cumin seeds and cook over moderately high heat for 5 seconds, just until sizzling. Add the leek and cook, stirring, until soft, about 1 minute. Add the ginger, coriander and ground cumin along with about 50ml of water and let cook until most of the liquid has evaporated, about 2 minutes.
To the lentils, add the green beans, kale, carrot and three-quarters of the coriander. Season with salt. Cook until the lentils and vegetables are tender, about 15 minutes.
Scrape in the spice paste and the remaining coriander. Simmer for 5 minutes, then serve.
Serve with brown rice.