Preheat the oven to 350 degrees F (175 degrees C).
Place carrots in a large roasting dish big enough to hold all the root vegetables. Drizzle with olive oil.
Bake in the preheated oven for 10 minutes.
Meanwhile, toss sweet potato with 1/4 tablespoon warm sunflower oil for 2 minutes to give it color. Add pumpkin and toss for 30 seconds. Add to carrots and roast until all vegetables are softened and the color has intensified, about 40 minutes.
While vegetables are roasting, heat remaining 1/4 tablespoon sunflower oil in a large pot over medium-high heat. Add onion and cook for 2 minutes. Add garlic and cook until fragrant, about 1 more minute. Stir in cumin, turmeric, and harissa; cook for 1 minute.
Remove vegetables from the oven and add to the pot. Pour in vegetable broth and bring to a boil. Reduce heat and simmer until vegetables are soft, about 10 minutes. Puree with an immersion blender to desired consistency. Season with salt and pepper.