Rinse the lentils a few times under cold running water to get rid of any extra starch.
Heat the oil in a pan on a low to medium heat and cook the cumin seeds for around a minute until a darker brown.
Add the turmeric and grated ginger and immediately pour in the water and add the yellow lentils. Boil on a low to medium heat for 30 minutes, stirring regularly, until the lentils are soft and cooked.
Add spinach leaves, thin ginger slices and salt to taste. If using coconut milk, add this at the end when the lentils are cooked and the water is absorbed.
Serve with rice and yoghurt or green coriander and cashew chutney.