In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 5 minutes until translucent.
Stir in the minced garlic, grated ginger, and red pepper flakes. Cook for an additional 1-2 minutes until fragrant.
Add the chopped carrots and vegetable broth to the pot. Bring to a boil, then reduce the heat and simmer for about 20 minutes, or until the carrots are tender.
Remove the pot from heat and let it cool slightly. Using an immersion blender, blend the soup until smooth. Alternatively, you can carefully transfer the soup in batches to a blender.
Stir in the miso paste and lime juice until well combined. Season with salt and pepper to taste.
Serve hot, garnished with fresh cilantro if desired.