To a heavy based saucepan, add the chopped onion, crushed garlic, ginger, lentils and 1½ litres water. Stir to combine. Bring the pot of ingredients to the boil and then turn the heat down to a simmer.
Stir in the ground turmeric and chilli, pop the lid on and simmer for twenty minutes. While the soup is cooking, boil the pumpkin for ten minutes until the pieces are tender but still firm. Drain the pumpkin and set aside.
For the onion topping, cut the onions into rings, and cook them in a frying pan with the groundnut oil.
While the onions are cooking, finely chop the garlic and chilli (remove the seeds) and add these to the onions. Cook these until the onions are golden brown.
Remove the lid from the pot of lentils and turn up the heat to boil for five minutes. Put the lentils with the pumpkin into a blender. Do this in batches, and blitz until smooth.
Add the chopped coriander to the soup and a generous amount of salt to taste.Serve warm with a good spoonful of the spicy onions on top.