Blend the steamed squash with the soy milk and the arrowroot or cornstarch until smooth. Set aside. Heat the oil in a saucepan. Saute the celery, carrots, onions, and seasonings for about 5 minutes. Add the squash mixture and continue cooking, stirring constantly until the sauce has thickened. Spoon the sauce over the cooked pasta. Variation: Substitute 1 1/2 cups broccoli florets for the celery and 1 cups quartered mushrooms for the carrots. Or you may wish to use these vegetables in addition to the celery and carrots.