Heat oil in a large saucepan over medium heat. Add onion and garlic; cook, stirring occasionally, until tender, 6-8 minutes. Add coriander, crushed red pepper, and ginger; cook, stirring, 1 minute. Stir in squash, broth, and lemon juice; bring to a boil. Reduce heat to a simmer and cook 10 minutes or until squash is tender.
Working in batches, transfer soup to a blender and blend until smooth (or blend in the pan with an immersion blender). To serve, drizzle soup with a small amount of olive oil and sprinkle with crushed red pepper, if desired.