Preheat oven to 400 F.
On a baking tray spread cauliflower florets, potatoes, and garlic cloves. Drizzle around 1/2 tbsp oil and sprinkle some salt and pepper. Give them a quick mix.
Then cook them in preheated oven for about 15 min. Using spatula stir the florets and potatoes and cook for another 10-15 min or until well done.
Once roasting is done allow it to cool down for some time.
Transfer everything to the blender. Add 2 cups of water and blend the florets until it forms a puree.
Heat remaining oil in a medium pot on low heat. Add turmeric and red chili flakes and cook for a few seconds.
Add the roasted cauliflower puree, some more water or vegetable stock and bring mixture to a boil. Then add lemon juice and more salt and pepper if necessary.
Cook the cauliflower soup on low heat for about 5 min and serve warm.