Graham Streusel Cake

My aunt has a recipe for Graham Streusel Cake that I adapted into a cupcakes.  These are the cupcakes pre-icing, but you get the idea, and now, you get the recipe. 
Graham Streusel Cake
1.  Make Cake:  1/4 c. vegetable oil, 3 eggs, 1 c. water, and a yellow cake mix.  Mix all ingredients together until blended. 
2.  Filling:  Mix 2 c. graham cracker crumbs, 3/4 c. chopped walnuts (optional), 3/4 c. brown sugar (packed), 1 1/4 t. cinnamon, 3/4 c. butter (melted).  Mix together. 

3.  Add 1/2 of the cake batter to the bottom of a 9x13x2 inch greased pan.  Top with 1/2 of the filling mix.  Add the rest of the cake batter.  End with the rest of the crumble. 
4.  Bake at 350 for 45 minutes. 
5.  Cool and drizzle with glaze.
Glaze:  1 c. powdered sugar, 1-2 T. water