Heat oil in a large skillet or saucepan. Cook onions, garlic, carrots and celery in oil for 3 to 5 minutes, stirring frequently. Stir in potatoes, cauliflower, green beans, corn, peas, soy sauce, and vegetable broth. Bring to a boil, then turn heat down to a strong simmer. Cook until vegetables are barely tender, about 5 minutes. Season with salt and pepper.
In a small bowl, mix the cornstarch and 1/4 cup water until cornstarch is completely dissolved. Stir into simmering vegetables, and continue simmering until sauce thickens, about 3 minutes.
Roll out 1/2 of the dough to line an 11x7 inch baking dish, or pie pan. Pour the filling into the pastry lined dish. Roll out remaining dough, arrange over the filling, and seal and flute the edges and slit the top to let steam escape.
Bake in preheated oven for 30-45 minutes, or until the crust is brown and sauce is bubbling through the slits in the top.