Preheat the oven to 356ºF.
Mix the oats, cornstarch, cocoa powder, cane sugar, baking powder, salt, and cinnamon in a bowl.
In a separate bowl, mix the oil, soy milk, and the grated pumpkin. Slowly add the wet mixture to the dry mixture.
Grease a baking dish or cake pan and add the cake mixture. Sprinkle with the chopped hazelnuts if desired.
Place in the oven for 35 to 40 minutes. Test the doneness by poking with a toothpick until it comes out dry
Remove the dish from the oven and cover it with a cloth to let it cool for a few minutes.
Unmold and cool on a rack before serving.