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