Preheat the oven to 400 degrees F (200 degrees C).
Place carrots and cauliflower in a casserole dish; toss with olive oil, garlic, salt, and black pepper.
Roast carrot mixture in the preheated oven for 20 minutes; stir and roast until vegetables are tender and slightly charred, another 25 minutes. Remove from the oven and stir.
Bring vegetable broth to a boil in a large pot. Stir in curry powder and add the roasted vegetables. Cover and boil soup until vegetables are soft, 8 to 10 minutes. Remove from heat.
Blend the soup with a potato masher or an immersion blender until smooth. Return pot to burner on medium heat. Stir coconut milk and lime juice into soup; simmer until heated through, 5 to 10 minutes.