Preheat oven to 350°.
In a large bowl, mix together the water, pumpkin, eggs, 1 Tablespoon of vanilla, and pumpkin pie spice, until well combined.
Add the cake mix and baking soda and mix until just combined.
Grease a 9×13 pan with butter or nonstick cooking spray, and pour batter into pan.
In a small bowl, mix together 1/2 cup of brown sugar, flour and melted butter. Use your fingers to sprinkle over the top of the cake.
Bake cake for 25-30 minutes, or until a toothpick inserted comes out clean.
While the cake is baking, start preparing your glaze.
Combine the other 1/2 cup brown sugar, granulated sugar, 1 teaspoon vanilla, and heavy cream in a saucepan and bring to a simmer.
Remove from heat and stir until all sugar is dissolved. This shouldn't take very long.
When cake is finished baking, poke holes in the top with a toothpick. Pour glaze over the cake. It should seep into the holes and make for a nice sticky, sweet topping.
Serve cake warm or at room temperature.