Preheat the oven to 425°F and spray a baking sheet with cooking spray.
Cut the butternut squash into large 2 inch chunks, and transfer them to the prepared baking sheet. Season with salt and pepper and cinnamon, Then drizzle with 1 tablespoon of the olive oil and maple syrup. Toss to combine.
Bake the butternut squash in the preheated oven for 40 minutes, flipping halfway through.
While the butternut squash is roasting, heat the remaining tablespoon of olive oil in a large soup pot. Add the onions and season with salt and pepper. Cook the onions until they soften and become translucent, about 4-5 minutes. Then add the garlic, and stir frequently until fragrant, about 30 seconds to one minute.
When the butternut squash is cooked and fork tender, transfer it to the pot with the onions and garlic mixture. Next, add the vegetable broth. Bring the contents of the soup to a boil, then cook on medium heat for 15 to 20 minutes, stirring occasionally.
Using an immersion blender, blend the soup until there are no more chunks of squash left. Stir in the oat milk. Serve hot with a dollop of yogurt and fresh thyme, if desired.