Preheat the oven to 350°F and grease your baking pan.
Make the streusel by combining brown sugar, flour, cinnamon, salt, and chopped nuts.
Add the melted and cooled butter and mix until coarse crumbs form. Set aside.
Prepare the cinnamon swirl by combining brown sugar, flour, and cinnamon in a small bowl.
In a medium bowl, whisk together flour, baking soda, baking powder, salt, and pumpkin pie spice.
In a large bowl, combine brown sugar, granulated sugar, and vegetable oil.
Add sour cream, eggs, vanilla extract, and pumpkin puree. Mix until well combined.
Gradually add the dry ingredients to the wet ingredients and mix just until combined. Do not overmix.
Spread half of the cake batter into the prepared pan.
Sprinkle the cinnamon swirl evenly over the batter.
Add the remaining batter and gently spread it into an even layer.
Sprinkle the streusel topping evenly over the cake.
Bake for approximately 45–55 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Allow the cake to cool before slicing and serving.
