Put the ginger and 4tbsp water into a blender to make a paste. Heat the oil in a large heavy-based pan and brown the chicken in batches. Leave to rest on a plate.
Add the onion and cook for 10 minutes, adding the garlic, coriander, chilli, spices, and salt, and cook for a few minutes.
Pop the chicken back into the pan with any juices from the plate, and add the water and lemon juice. Put a lid on the pan and cook for 15 minutes. Turn the chicken, then cook for another 15 minute The chicken will melt off the bone when it's ready.