Preheat oven to 400°F (200°C). Toss cauliflower florets with 1 tablespoon olive oil, salt, and pepper. Spread on a baking sheet in a single layer and roast for 20-25 minutes, or until tender and slightly browned.

While cauliflower is roasting, heat the remaining 1 tablespoon olive oil in a large pot or Dutch oven over medium heat. Add onion and carrots and cook until softened, about 5-7 minutes. Add garlic and ginger and cook for another minute until fragrant.

Stir in curry powder, turmeric, and red pepper flakes (if using) and cook for 1 minute more. Pour in vegetable broth, scraping up any browned bits from the bottom of the pot.

Add the roasted cauliflower to the pot. Bring to a simmer and cook for 10 minutes to allow the flavors to meld. Remove from heat and let cool slightly. Carefully blend the soup using an immersion blender or transfer to a regular blender in batches until smooth and creamy.

Return the soup to the pot and stir in coconut milk. Heat through gently, being careful not to boil. Season with additional salt and pepper to taste. Serve hot, garnished with fresh cilantro and a squeeze of lime juice, if desired.