Preheat the oven to 350ºF.
Prepare a 9x13 baking pan by spraying it with cooking spray.
In a large mixing bowl, combine the cinnamon, salt, baking powder, flour, sugar, milk and eggs.
Combine well, then add in ½ of the diced apples and stir well.
Slowly drizzle the melted butter into the batter while continuing to mix on low.
Pour batter into the prepared pan.
Sprinkle the remaining apple pieces onto the top of the batter.
In a separate bowl, mix together the ingredients for the topping and combine well.
Place scoops of this thick mix over the batter.
Take a butter knife and run it through the thick batter and the cake to give it a marble effect.
Bake for 45-50 minutes until a toothpick inserted in the middle comes out clean.
In a small bowl, combine glaze ingredients until smooth.
When the cake cools completely, drizzle the entire top of the cake with the glaze.