Soak the lentils in cold water for at least an hour, preferably overnight. Rinse, drain and set aside.
Thinly slice the onion. Heat the oil in a large, heavy-based pan over medium-low heat. Add the onion and gently cook for 10 minutes until soft and slightly caramelised.
Add the tomatoes, spices, salt and turn up the heat to medium-high. Cook for 5 minutes until the liquid has reduced to a sticky sauce.
Add the boiling water, chana and ginger. Bring to the boil, cover with a lid, then reduce the heat and gently simmer for 60-90 minutes, stirring occasionally. The cooking time depends on how long you soaked the lentils for - it’s ready when the lentils are tender.
Remove and discard the ginger.
If you want a thick, creamy pottage, blitz the dal for a few seconds with a stick-blender. If you want a thinner soup, add more boiling water and adjust the seasoning.
Serve with fresh coriander leaves scattered on top, a pinch of paprika and lemon wedges on the side.