Place the lentils in a small pan with the hot vegetable stock and place over a medium-high heat. Cook for 15 minutes
Meanwhile, add a splash of vegetable oil to a saucepan and sweat the onion, garlic and carrot with a pinch of salt until soft but not colored (about 5 minutes)
Add the spices, tomato puree and harissa and stir for a minute or two, then add the tinned tomatoes
When the lentils are just cooked, add them to the pan of vegetables (including any remaining stock). Leave to simmer for 30 minutes or until the sauce has reduced down and is just clinging to the lentils