Wash squash well, cut in half lengthwise, remove seeds and rub each section with oil. Place cut side down on cookie sheet or in glass baking dish and roast 25 minutes or until soft throughout. Remove from heat and set aside.
In Dutch oven or large pot over medium heat, sauté onion in olive oil until soft (about 3 minutes). Add carrots, celery and mirin and sauté 3 minutes. Cut green beans into bite-size pieces, add to pot along with corn and sauté 5 minutes or until beans start to soften. Chop squash into bite-size pieces and fold into mixture.
In small bowl, whisk together water, liquid aminos and arrowroot until smooth. Pour into pot with vegetables and stir until liquid starts to thicken. Season to taste with pepper. Remove from heat and transfer to deep casserole.
Crumble pie crust over top of casserole and cover with foil. Bake 30 minutes. Remove foil and bake 8 minutes longer or until top is lightly browned. Remove from oven and serve.