In a large pot, heat olive oil over medium-low heat. Add onions; sauté until softened and translucent, 3 to 4 minutes.
Add garlic, and cook 1 minute more. Add ginger and curry powder and cook 1 minute more, until fragrant.
Add cauliflower florets, carrots and sweet potato to pot, stirring to coat vegetables with spice mixture.
Stir in broth and salt, pepper, onion powder, garlic powder, and parsley flakes. Partially cover pot, reduce heat and simmer for 20 minutes or until vegetables are tender.
Purée the soup in batches in a blender, then taste and adjust seasoning if necessary. If desired, serve topped with Greek yogurt and cilantro.