Put the chickpeas, onion, garlic and stock in a saucepan and bring to the boil. Reduce the heat to low and simmer for 20 minutes or until the chickpeas are starting to fall apart.
Ladle about one-third of the soup into a blender or food processor and purée it until smooth. Return the puréed soup to the pan and bring back to simmering point. Add the asparagus, cover with a lid and cook gently for 5–6 minutes or until the asparagus is just tender.
Meanwhile, cook the orzo in a large saucepan of boiling water according to the packet instructions. Drain the pasta and add it to the soup, with pepper to taste.
Put the lemon zest and parsley in a small bowl and mix together. Top each bowl of soup with a small spoonful of the lemon and parsley mixture and serve immediately, offering lemon wedges so that the juice can be added to the soup to taste.