Preheat the oven to 180°C.
Peel the squash, remove the seeds and cut the flesh into cubes. Cut the tomatoes in half, peel the garlic, chop the carrots.
Put all the prepared vegetables in a roasting tray , drizzle with the oil, sprinkle with the spices, season with salt and pepper, then cover with foil and bake for about 1 hour, or until soft.
When the vegetables are soft and slightly caramelized, transfer everything back into the saucepan. Add half of the stock and process with a hand-held blender until smooth.
Add the lentils and the remaining stock. Bring to the boil then simmer for 20 minutes until the lentils soften.
Serve it with a dollop of yogurt and a pinch of sumac.
Serve with pita or flatbread.