Heat the oil in a large saucepan over medium-high heat. Add squash, onion, celery, pepper, and garlic; sauté for 5 minutes. Add remaining ingredients; bring to a boil. Cover, reduce heat, and simmer 25 minutes or until tender. Discard bay leaf.
Place half of the squash mixture in a blender, and process until smooth. Pour pureed mixture into a bowl; repeat procedure with remaining squash mixture. Return pureed mixture to pan; cook over medium heat 3 minutes or until heated.