Heat the oil over medium heat. Add the spices and cook, stirring, for 1 minute. Add the ginger and stir for another minute.
Add the onion, carrots and lime zest. Sprinkle with 1 teaspoon of salt to taste, and cook until the onions begin to soften, about 5 minutes.
Add the broth and bring to a boil. Reduce heat to medium low and simmer for about 30 minutes, until the carrots are very soft.
Remove from heat and allow to cool briefly. Puree the soup in batches in a blender, or use an immersion blender, until the soup is smooth and silky. If the soup is too thick, add broth and stir until the right consistency is reached.