Heat the oil in a large pot over medium heat. Add the chopped onion and cook until translucent, about 5 minutes.
Add the minced garlic and grated ginger and cook for another 2 minutes.
Add the chopped carrots, vegetable broth, ground coriander, salt, and black pepper. Bring to a boil.
Reduce the heat to a simmer and cook until the carrots are tender, about 20-25 minutes.
Use an immersion blender to puree the soup until smooth. Alternatively, transfer the soup to a blender in batches and blend until smooth.
Stir in the coconut milk, if using, and adjust seasoning with more salt and pepper if needed.
Serve hot, garnished with fresh herbs if desired.