Preheat oven to 350 degrees and arrange rack to the center of the oven. Line a 9x9 pan with parchment paper and set aside.
In a large bowl, whisk flour, sugar, baking powder, baking soda, salt and spices together very well.
In a separate bowl, whisk vegetable oil, pumpkin puree, buttermilk, eggs and vanilla until combined. Make a well in the center of the dry ingredients, and pour in the wet ingredients. Mix until just incorporated as you do not want to over-mix the batter. Pour batter into prepared pan and set aside.
For the crumble, toss sugar, flour, salt, cinnamon and nutmeg together in a large bowl. Stir in melted butter until crumbly. It will still be wet but you will be able to break it up into smaller pieces. If for some reason it won't crumble, add another tablespoon of flour to the mixture. Crumble the topping over the batter in the pan into an even layer. Bake for 35-40 minutes OR until a toothpick inserted in the center comes out clean.
While cake is cooling, prepare glaze. In a small bowl, combine confectioner's sugar, maple syrup and cream until smooth. Add more or less cream for your desired thickness - I like mine on the thicker side so it doesn't melt into the cake.