Preheat oven to 375. Prepare a 10" tube pan with cooking spray and flour; set aside. To prepare filling, combine two tablespoons cake mix, brown sugar, cinnamon, and walnuts in a small bowl; set aside. To prepare cake, combine remaining cake mix, eggs, sour cream, water, oil and granulated sugar in a mixing bowl. Pour two thirds of batter into prepared pan. Sprinkle with filling mixture. Spoon remaining batter evenly over filling mixture. Bake for 55 minutes. Cool in pan 25 minutes. Then, invert onto serving plate. Cool. To prepare glaze, combine powered sugar and milk in a small bowl. Stir until smooth. Add more milk to thin glaze as needed. Drizzle over cake.