Slice onions finely and brown in the oil. Then add garlic and ginger and cook for about three minutes. If the onions get too dry add a little liquid from the lentil pot. Chop the tinned tomatoes and add to the onion mix. Cook for a few minutes, then add all the ingredients except for the coriander. Gently cook this for about 15 minutes. Taste and add salt if necessary. Now add the sauce to the lentils, add the fresh coriander, stir and let it idle along for about 5 minutes.
You can keep this in a non-metal container in the refrigerator for quite a while.