Rinse the red lentils in cold running water, then drain.
In a pan over a moderate heat, cook the onions and celery in the oil for about 10 minutes, until soft. Add the garlic and cook for two minutes more. Add the spices and stir to toast. Add the lentils and tomatoes and bring to a simmer.
Add a litre of cold water and bring to the boil. Season well. Reduce to a moderate heat and cook for about 30 minutes, until the lentils have collapsed. Add more boiling water if you would like a thinner soup.
Remove from the heat and blend half the soup, adding the blended portion back to the pan and stirring well to mix. Check the seasoning.
Fry the pumpkin seeds and cumin seeds in the olive oil until just beginning to pop. Add a good pinch of salt and remove from the heat.
To each bowl of soup add a spoonful of the toasted pumpkin and cumin seed oil, some crumbled feta, a drizzle of the pomegranate molasses and a big pinch of chilli flakes.