Preheat the oven to 200°C.
Peel the squash, cut it in half, remove the seeds and the soft tissues. Cut the flesh roughly into 3 cm pieces, then scatter them on a baking sheet.
Peel and core the apple then cut into wedges and add to the squash. Drizzle with 1 Tbsp of oil, season with salt and pepper, then rub them thoroughly.
Bake in the oven for 25-30 minutes until soft.
Meanwhile, chop the onion and celery and sauté them in the remaining oil. Add the spices and stir for 1 minute, then add the roasted pumpkin and apple. Stir for another minute, then pour over the stock. Bring to the boil and simmer for 20 minutes.
Using a blender, process the soup until creamy and silky.
Serve with pumpkin seeds sprinkled on top and with a spoonful of Greek yoghurt if you like.