Preheat oven to 375 degrees. Place butternut squash, onions, pears, garlic and lemon zest in a large roasting dish. Avoid overlapping vegetables as much as possible. Sprinkle with salt, black pepper, cayenne pepper and fresh sage. Drizzle with olive oil and mix well to coat vegetables with oil. Cover and roast for 45 minutes, until butternut squash softened. Remove cover and roast an additional 15 minutes. Remove from oven and allow to cool slightly before food processing. Add about 1/4-1/3 of vegetables to food processor with enough vegetable broth to puree into a smooth soup texture. Continue to process aliquotes of vegetables with broth until all vegetables pureed. Transfer puree to a heavy soup pot. Simmer for at least 30 minutes to blend flavors. Add salt and pepper to taste and simmer at least 5-10 more minutes. Serve warm, sprinkled with chopped cilantro or parsley.