Preheat oven to 400°.
Combine first three ingredients in a large bowl; toss well. Place pumpkin mixture on a baking sheet coated with cooking spray. Bake at 400° for 30 minutes or until tender.
Heat a large Dutch oven over medium-high heat. Coat pan with cooking spray. Add onion; sauté 8 minutes or until tender. Add garlic; sauté 1 minute. Add pumpkin mixture, 4 cups water, and remaining ingredients; bring to a boil. Reduce heat, and simmer 20 minutes.
Place half of pumpkin mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Pour into a large bowl. Repeat procedure with the remaining pumpkin mixture.