Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan and line with parchment paper, leaving a little overhang for easy removal.
In a large bowl, sift together flour, baking powder, baking soda, salt, and spices.
In a separate bowl, whisk together pumpkin purée, Greek yogurt, oil, both sugars, eggs, and vanilla. Add the wet ingredients to the dry and mix until just combined. Do not overmix.
In a medium bowl, blend together flour, cocoa powder, baking powder, salt, and espresso powder if using.
In another bowl, whisk together milk, sugar, oil, egg, and vanilla. Stir wet into dry until smooth and glossy.
Alternate scoops of pumpkin and chocolate batter into the loaf pan. Use a butter knife to gently swirl the batters together in a figure-8 motion for a marbled effect. Don’t over-swirl.
Bake for 50–60 minutes, or until a toothpick inserted in the center comes out mostly clean (a few moist crumbs are fine).
Let cool in the pan for 10–15 minutes, then lift out and cool completely on a wire rack.
Place the chocolate chips and cream in a microwave safe bowl, and melt them in the microwave in 20 second bursts, stirring well each time.
When most of the chocolate has melted, stir until smooth. It should only require a minute or two. Add Vanilla and stir until smooth.
Once the cake is fully cooled, pour ganache over the top. Use a spatula to gently nudge it toward the edges for a natural drip effect. Let ganache set before slicing.