In a pot, over medium heat, add butter, once melted, add cinnamon, mix well, add cubed butternut squash, apples, brown sugar, and water, mix until combined. Cover and stir on occasion, until butternut squash and apples are slightly soft.
Add cornstarch and water mixture, Stir well. Add to Butternut squash mixture, continue stirring, cook until butternut squash and apples are soft, and the filling has thickened. Bring to a boil and let cool.
Add the butternut squash filling, and walnuts in pie base, brush egg wash on edges, top with other pie crust, and fork edges, to seal. Brush egg wash on top of pie.
Place in oven at 350 degrees for 15 minutes, until warmed and butternut squash is crisp on the top. Remove from oven, sprinkle cinnamon on top and ready to serve.