Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a frying pan, add the onion and fry, stirring, for 5 minutes or until just beginning to turn golden.
Stir in the garlic and chorizo and cook for 2 minutes. Mix in the paprika, add the thyme, stock and tomato purée and bring to the boil, stirring, then add a little salt and pepper.
Add the sweet potatoes and chickpeas to the slow cooker pot and pour over the hot stock mixture. Cover with the lid and cook on low for 6–8 hours until the sweet potatoes are tender.
Ladle into bowls, sprinkle with a little chopped parsley or extra thyme and serve with warm pitta breads, if liked.