Heat the large pot over medium heat and add the olive oil. Once shimmering, add the chopped onion and sauté until translucent and fragrant, about 5 minutes.
Add the minced garlic to the pot and cook for another 30 seconds until fragrant, being careful not to burn it.
Stir in the diced pumpkin and cook for a few minutes, allowing the pumpkin to soften slightly and absorb the flavors.
Pour in the vegetable broth, bring the mixture to a gentle simmer, and cook uncovered until the pumpkin is tender, about 15-20 minutes. You should see the pumpkin break down easily with a spoon.
Use an immersion blender directly in the pot or carefully transfer the soup to a blender in batches. Blend until smooth and creamy, with no lumps remaining.
Stir in the coconut milk, chopped Thai basil, and lime juice, mixing well to combine. Heat just until warmed through, about 2-3 minutes. Taste and season with salt and pepper as needed.
Serve the soup hot, garnished with additional Thai basil or a squeeze of lime if desired.
