Preheat oven to 350 degrees and grease a 9×13 pan well.
In a small bowl combine the apple pie filling and cinnamon; set aside.
In another small bowl combine the brown sugar and nuts. Don’t add the butter yet; set aside.
In large bowl combine flour, sugar, milk, ½ cup butter, eggs, baking powder and salt. Mix on low until barely combined and then on medium for 2 minutes.
Pour ½ of the batter into prepared pan. Spoon ½ of the pie filling evenly over batter. Spread ½ of the brown sugar mixture evenly over pie filling.
Pour remaining batter to pan and spoon remaining pie filling over top.
Now mix the 3 Tablespoons of melted Butter with the remaining brown sugar mixture. Sprinkle evenly over top of cake.
Bake 45-50 minutes until tester comes out clean. Let cake cool for 20 minutes before adding the glaze below.
For the Glaze: Combine the powdered sugar, butter, and vanilla. Gradually add the hot water until the mixture is smooth and desired consistency is reached. Add more if needed. Drizzle over cake.