Heat the coconut oil in a large pot over medium heat. Add the diced onion and cook for 4 minutes until it softens.
Stir in the minced garlic and grated ginger. Cook for 1 minute until fragrant.
Add the red curry paste and stir for 30 seconds to coat the vegetables.
Add the cubed sweet potatoes, vegetable broth, coconut milk, and salt. Bring the mixture to a boil.
Reduce the heat to low, cover the pot, and simmer for 20 minutes until the sweet potatoes are fork-tender.
Use an immersion blender to puree the soup until smooth, or blend in batches in a countertop blender.
Stir in the lime juice. Serve hot with fresh cilantro on top.