To roast the butternut squash, preheat the oven to 400 degrees F. In a large bowl, toss the squash and 1 tablespoon olive oil. Season with salt and pepper. Arrange squash on a baking sheet in a single layer. Roast for 25 minutes or until squash is tender. Remove from oven and cool slightly.
Heat the remaining oil in a 6-quart saucepan over medium-high heat. Add garlic, carrots and onion. Cook, stirring occasionally, about 12 to 14 minutes or until slightly caramelized. Stir in cumin, chile flakes, paprika, and roasted squash. Cook for 1 to 2 minutes. Add stock and lentils. Bring to a boil, then reduce heat to medium-low. Cook, slightly covered, for 20 minutes or until lentils are very tender. Cool slightly then, working in batches, use an immersion blender to purée soup until smooth. Garnish with parsley, pepitas and yogurt, as desired. Serve immediately.