Heat the oil in a heavy-based saucepan over a medium heat, add the onion, garlic, celery and green pepper and fry gently for 10–12 minutes or until softened and beginning to colour.
Stir in the lentils and spices and cook for 2–3 minutes, stirring frequently. Add the tomato purée, stock and chickpeas and bring to the boil. Reduce the heat, cover and simmer gently for about 20 minutes or until the lentils collapse. Season with salt and pepper to taste.
Ladle into bowls and sprinkle with the coriander. Serve immediately with boiled brown rice and cooling, spiced yogurt (see below).