Put the onion, garlic and parsley in a food processor or blender and process until finely chopped.
Heat the oil in a saucepan and cook the onion mixture over a low heat until slightly softened. Add the chickpeas and cook gently for 1—2 minutes.
Add the stock, season well with salt and pepper and bring to the boil. Cover and cook for 20 minutes or until the chickpeas are really tender.
Allow the soup to cool for a while, then partly purée it in a food processor or blender or mash it with a fork so that it retains plenty of texture.
Pour the soup into a clean pan, add the lemon juice and adjust the seasoning if necessary. Heat through gently. Serve the soup topped with grated lemon rind and cracked black pepper.