In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and grated ginger, cooking for an additional 1-2 minutes until fragrant.
Add the cubed butternut squash to the pot, followed by the red curry paste. Stir well to coat the squash and cook for 2-3 minutes to enhance the flavors.
Pour in the vegetable broth and bring the mixture to a boil. Once boiling, reduce the heat and let it simmer for 15-20 minutes or until the squash is tender.
Remove the pot from the heat and carefully blend the soup using an immersion blender until smooth. Alternatively, you can blend the soup in batches using a regular blender.
Return the blended soup to the pot, stir in the coconut milk and lime juice, and heat gently over low heat. Season with salt and pepper to taste.
Serve warm, garnished with fresh cilantro if desired.