Preheat the oven to 350°F. Lightly grease an 8"square pan or 9" round pan.

To make the topping: Whisk together the sugar, salt, flour, spice, and nuts. Add the melted butter, stirring just until well combined. Set the topping aside.

To make the filling: Mix together the brown sugar, spice, and cocoa powder. Note that the cocoa powder is used strictly for color, not flavor; leave it out if you like. Set it aside.

To make the cake: Beat together the oil, eggs, sugar, pumpkin, spices, salt, and baking powder until smooth. Then add the flour, stirring just until smooth.

Pour/spread half the batter into the prepared pan, spreading it all the way to the edges. If you have a scale, half the batter is about 13 1/2 ounces.

Sprinkle the filling evenly atop the batter.

Spread the remaining batter atop the filling. Use a table knife to gently swirl the filling into the batter, as though you were making a marble cake. Don't combine filling and batter thoroughly; just swirl the filling through the batter.

Sprinkle the topping over the batter in the pan.

Bake the cake until it's light brown on top, and a toothpick or cake tester inserted into the center comes out clean, about 40 to 45 minutes.