Preheat the oven to 400°F. Spread the squash cubes, chopped apples, and onion on a baking sheet. Drizzle with olive oil, then sprinkle with cinnamon, salt, and pepper. Toss to coat evenly.
Roast the vegetables for 25 to 30 minutes until the squash is soft and the edges begin to brown.
Transfer the roasted mixture to a large pot. Add the minced garlic and cook over medium heat for 1 minute until fragrant.
Pour in the vegetable broth. Bring the mixture to a gentle simmer and cook for 5 minutes.
Remove the pot from the heat. Use an immersion blender to puree the soup until completely smooth. If using a countertop blender, work in batches and return the soup to the pot to warm briefly before serving.