Preheat oven to 180C and line a baking tray with parchment paper. Arrange cauliflower florets, potatoes and onions on the prepared baking tray.
Peel and discard the papery outer layers of the whole garlic bulb and cut 1/4 from the top of cloves. Add garlic to the tray with the rest of the vegetables. Drizzle everything with oil and sprinkle with spices.
Pop in the oven for 30-40 minutes or until the vegetables are tender and the garlic is soft. Add all the vegetables into a blender with walnuts, water/vegetable stock and puree into a creamy texture, add more stock/water if the soup is too thick. Garnish with fresh coriander and seeds, serve and enjoy right away.