Heat the olive oil and cayenne pepper in a large pot over medium heat; saute the onion until tender. Season with curry powder. Pour in the stock and mix in the potatoes. Bring to the boil, reduce heat to low and simmer 20 minutes or until potatoes are very tender.
Mix the courgettes and cauliflower into the pot and continue cooking 30 minutes.
Mash the chickpeas with a fork and mix into the pot. Continue cooking 5 minutes, until heated through. Top with yoghurt and garnish with coriander to serve.