Preheat oven to 425°.  

Heat vegetable stock over medium heat in a large cast-iron skillet. Cook onions, mushrooms, and garlic in stock for 3 to 5 minutes stirring frequently. Stir in carrots, parsnips, potatoes, and celery.  If the vegetables begin to stick, add additional stock one tablespoon at a time if needed.  

Add spices and cook for 2 minutes. Stir in green beans. Sprinkle the flour over the top of the vegetables and cook 2 minutes, until the white disappears (the vegetables will seem dry). Slowly pour in the milk, adding a few splashes at a time, stirring constantly, scraping any brown bits from the bottom of the pan.  Add vegetable stock, soy sauce, and pickapeppa sauce. Bring to a low boil.

Continue to let bubble until thickened, about 3 to 5 minutes, stirring very often and scraping a spatula along the bottom of the pot to prevent sticking. Then turn the heat down and simmer for about 10 minutes, or until vegetables are barely tender.  Season with salt and pepper.  Remove from heat and let cool for about 5 minutes. 

Roll the pie dough into a circle large enough to cover your cast iron pan. Brush the edges of the cast iron with the coconut oil and maple syrup wash, then lay the dough over the top to overhang the sides. Trim the overhang to a 1/2 inch larger than the edge of the pan. Gently press the dough onto the sides of the pan so that it sticks, then brush all over with the remaining wash. With a sharp knife, cut five slits in the top.
Carefully place the cast iron in the oven. Bake until the pie is hot and bubbly on the inside, and the crust is deeply golden, about 20 to 25 minutes, rotating the pan 180 degrees F halfway through. Let rest a few minutes. Serve hot.