Preheat the oven to 350°F. Spray a 9×13 pan with non-stick cooking spray. (For a thicker cake use a 9×9 pan; a 9x13 was used in this photo)
To make the topping, combine the flour, brown sugar, pumpkin spice and butter into a small bowl. Mix with a fork until it resembles crumbles. You may need to use your hands to combine. Set aside.
In a large bowl, combine the flour, sugar, baking powder, baking soda, pumpkin spice, cinnamon and salt. Add in the pumpkin, milk and whisked egg. Stir just until combined. Pour into the prepared pan and then evenly top with the crumb mixture.
Bake coffee cake for 25-30 minutes, or until a toothpick comes clean. Allow to cool. Combine the glaze ingredients in a small bowl and drizzle over the top if desired.