Preheat your oven to 350°F (175°C) and grease/flour a 10-12 cup bundt cake pan.
In a large mixing bowl, combine flour, sugar, cocoa powder, baking powder, baking soda, salt, cinnamon, nutmeg, and cloves. Whisk to blend.
In another bowl, mix vegetable oil, pumpkin puree, eggs, vanilla extract, and yogurt until smooth.
Combine wet and dry ingredients, fold in chocolate chips, and pour the batter into the bundt pan.
Bake for 45-55 minutes, until a toothpick comes out clean when inserted.
Let the cake cool in the pan for 10 minutes, then transfer to a cooling rack to cool completely.
Melt semi-sweet chocolate chips with butter and heavy cream, drizzle it over the cooled cake, and sprinkle chopped walnuts for a delightful crunch and rustic charm.