1. Preheat oven to 425 degrees F. In a large bowl, toss carrots, canola oil, coriander, cumin, mustard seeds, and salt and pepper to taste. Turn carrots out onto baking sheet lined with aluminum foil and roast, stirring occasionally, until carrots are tender and well-browned, about 40 minutes. Remove tray from oven.2. Heat olive oil in a large, heavy-bottomed saucepan. Add onion and cook, stirring occasionally, until onions are soft but not browned. Add garlic and ginger and cook, stirring constantly, until fragrant. Add carrots and stock, cover, and bring to a boil. Lower heat to medium-low and simmer soup, partially covered, until carrots have absorbed cooking liquid.3. Remove soup from heat and use a hand blender to blend until mostly smooth. Add yogurt and lime juice and blend until totally smooth.4. Let soup cool at room temperature for one hour, stirring occasionally. Transfer to refrigerator and let cool, stirring occasionally, until well chilled, about 45 minutes. Garnished with cilantro leaves and serve cold.