Gather the ingredients. Preheat the oven to 425 degrees F (220 degrees C).

Heat oil in a large skillet or saucepan. Add mushrooms, onions, and garlic; cook for 3 to 5 minutes, stirring frequently. Stir in carrots, potatoes, and celery. Stir in cauliflower and green beans; add vegetable broth and bring to a boil. Reduce heat and simmer until vegetables are just tender, about 5 minutes. Season with salt and pepper.

Mix water, cornstarch, and soy sauce in a small bowl until cornstarch is completely dissolved; stir into vegetables and cook until sauce thickens, about 3 minutes.

Roll out 1/2 of the dough to line an 11x7-inch baking dish. Pour vegetable filling into the pastry-lined dish. Roll out remaining dough; arrange over filling, then seal and flute the edges.

Bake in preheated oven until pie is golden brown on top, about 30 minutes.