Combine all ingredients EXCEPT food coloring, in the bowl of a freestanding mixer (or a mixing bowl if using a handheld mixer). Mix on high to fully combine. Glaze should be a medium texture allowing drizzling. If desired, add food coloring to tint the glaze orange (1 part red to ¾ parts yellow).
Once the cake is fully cooled, if the flat sides of the cake halves are very uneven, a serrated knife can be used to make each flat side of the cake even.
Place the bottom half of the cake on a firm surface with the decorative side facing down (the flat inside half facing upwards). With a large spoon, gently create a hollow in the bottom half of the cake (from the flat side) leaving a boundary of 1 1/2 inches around the sides and bottom of the cake to maintain the structure (or is could break). {see photo below}
Place the top half of the pumpkin on a firm surface with the decorative side down (the flat half of the cake facing upwards). With a large spoon, create a hollow out an inch indentation in the top of the cake. The candy inside the cake will be rounded at the top and having a portion of the top of the cake scooped out will allow more candy to fit inside the cake.
In a mixing bowl, combine all selected Halloween candy and mix well!
Place the bottom of the cake, decorative side down on serving plate. Scoop candy into the indentation of the bottom pumpkin half, mounding the candy at the top.
With a kitchen knife or frosting spreader, spread a layer of chocolate ganache along the flat edge of the bottom half of the pumpkin cake. This is designed to seal the cake so the ganache layer does not need to be overly thick. My goal was to not see it. Gently place the top of the pumpkin, flat side down, on top of the ganache careful to match the outside pattern of the pumpkin between the top and bottom layers.