Preheat the oven to 180°C / Gas Mark 4.
Place the cauliflower florets, chopped onion and garlic cloves on a large baking tray. Drizzle over the oil and sprinkle with the cumin and coriander.
Toss until everything is fully and evenly coated. Roast for 20-30 minutes until just beginning to brown.
When the cauliflower has roasted, remove from the oven.
Tip the cauliflower, onion and garlic mix into a large saucepan and add the vegetable stock and kale. Bring to the boil and simmer for 10-12 minutes until tender.
Add the lemon juice.
Using a stick blender or processor, purée the soup until smooth. Taste and adjust seasoning as necessary. Add more liquid if you prefer a thinner soup.
To serve drizzle with yogurt and sprinkle with chopped parsley