Preheat oven to 350 degrees F. Spray a 9x13-inch baking pan with cooking spray.
In a large bowl, whisk together flour, baking powder, salt, sugar, cinnamon, nutmeg, cloves and ginger. Add pumpkin, oil and vanilla. Stir with a spatula until combined. Batter will be thick. Spread batter evenly into the bottom of prepared pan.
For Topping: Whisk together brown sugar and cinnamon. Sprinkle evenly over batter. Pour hot water over the top.
Bake for 50 to 55 minutes, uncovered. (The cake will rise to the top and the sauce will be in the bottom.) Remove from oven and let stand 5 minutes before serving.
Serve each serving with a scoop of vanilla ice cream and chocolate chips, if desired. Enjoy!