Clean the Brussels sprouts and simmer in salted water for 5 minutes, then rinse in cold water.
Heat the oil and fry the onions in it until translucent, add the curry powder and roast briefly, then deglaze with the stock. Add the lentils, cinnamon stick and Brussels sprouts and simmer for about 15 minutes. Stir in the mango chutney and yoghurt and bring to the boil again briefly, adding a little more stock if necessary. Season to taste with salt and pepper.