Preheat oven to 350 degrees Fahrenheit. Spray a 9x13 inch pan with cooking spray.
Make the streusel:
In a medium bowl, combine the graham cracker crumbs, nuts, brown sugar and cinnamon. Stir in the melted butter. Set aside.
Make the cake:
In a large mixing bowl, combine the cake mix, water, oil, eggs, vanilla and cinnamon. Beat on low speed with an electric mixer just until moistened. Beat on medium speed for 2 minutes longer.
Spread 1/2 of the batter into a greased 9x13 inch pan.
Sprinkle on 1/2 of the streusel mixture. Carefully spread the remaining 1/2 of the cake batter over the streusel, and sprinkle with the remaining streusel.
Bake for 35 to 40 minutes or until a toothpick inserted comes out clean.
Make the frosting:
In a small bowl, combine confectioners sugar with vanilla and butter flavoring.
Add a few drops of water until you achieve drizzling consistency.
Cool slightly, then drizzle with the powdered sugar icing. Best if served warm.
Makes 12 to 16 servings.
The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**