Preheat your oven to 400°F (200°C). Place the diced sweet potatoes on a baking sheet and drizzle with olive oil. Toss to coat evenly, then spread them out in a single layer.
Roast the sweet potatoes in the preheated oven for 20-25 minutes, or until they are tender and lightly browned around the edges.
In a large pot or Dutch oven, heat a tablespoon of olive oil over medium heat. Add the diced onion and cook for 5-7 minutes or until softened and translucent.
Add the minced garlic and grated ginger to the pot, and cook for an additional 1-2 minutes, or until fragrant.
Stir in the red curry paste and cook for another minute, stirring constantly to toast the spices.
Add the roasted sweet potatoes to the pot, along with the coconut milk and vegetable broth. Stir to combine, then bring the soup to a simmer.
Let the soup simmer for 10-15 minutes to allow the flavors to meld together.
Use an immersion blender or transfer the soup to a blender, and blend until smooth and creamy.
Season the soup with salt, pepper, and lime juice to taste. Adjust the seasoning as needed.
Serve the Red Curry Sweet Potato Soup hot, garnished with chopped cilantro, chopped peanuts, and a drizzle of coconut milk, if desired.