Preheat your oven to 350°F & grease your 6 cup capacity bundt pan very well with professional bakery pan grease Combine the vinegar with the soy milk (soy milk is the only milk that will thicken)
In a larger mixing bowl combine the oil, brown sugar, salt, pumpkin & then the thickened vinegar/plant milk & whisk to combine well
Sift the flour with all the spices and the baking soda & add it all at once to the wet mixture in the bowl. Whisk smooth
In a small bowl combine the cocoa powder with the brown sugar & the hot water, whisk to a smooth paste, add ¼ cup of the batter to this & whisk smooth
Pour the a portion of the pumpkin batter into the well greased pan then spoon some of the chocolate marbling mixture over that. Add the remaining pumpkin batter over that & then the rest of the chocolate marble.
With a skewer or a thin knife, marble through the batter in the pan in a swirling technique
Bake immediately in the preheated 350°F oven for 20 minutes
Then turn the oven temperature down to 300°F & bake for another 20-30 minutes or when a toothpick inserted into the center comes out clean
Cool the pumpkin cake in the pan until you can touch it without burning your fingers, then turn it out onto a cooling rack to cool all the way
Glaze with confectioners sugar glaze or chocolate ganache or serve plain!