Preheat the oven to 400°F (200°C). Spread the pumpkin chunks on a baking sheet, drizzle with olive oil, and toss to coat evenly.
Roast the pumpkin in the oven for about 35-45 minutes, or until the edges are caramelized and the flesh feels tender when pierced with a fork.
While the pumpkin roasts, heat a large pot over medium heat. Add chopped onion and cook until translucent and fragrant, about 5 minutes.
Add the minced garlic to the onions and cook for another minute until fragrant, being careful not to burn it.
Once the pumpkin is roasted and cooled slightly, add the chunks to the pot with the sautéed onion and garlic.
Pour in the vegetable broth, then bring the mixture to a gentle simmer. Add cinnamon, salt, and pepper to taste.
Simmer the soup uncovered for about 10-15 minutes, allowing flavors to meld and pumpkin to soften further.
Use an immersion blender directly in the pot to blend the soup until it reaches a chunky yet smooth consistency, or transfer in batches to a blender and blend carefully.
Taste and adjust seasoning with additional salt and pepper if needed.
Serve the soup hot, garnished with a drizzle of olive oil or a sprinkle of fresh herbs if desired.
