Preheat oven to 350°F. Grease and line a 9x9-inch baking pan with parchment paper.
In a medium bowl, mix flour, sugars, cinnamon, pumpkin pie spice, and salt. Stir in the melted vegan butter until large crumbs form. Set aside.
In a separate bowl, whisk flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice.
In a large mixing bowl, beat the vegan butter (or oil), brown sugar, and granulated sugar until combined and slightly fluffy.
Stir in the pumpkin purée, dairy-free yogurt, milk, and vanilla until smooth.
Add the dry mixture to the wet mixture and stir gently until just combined. Do not overmix.
Spread half the batter evenly into the pan. Sprinkle with ⅓ of the streusel. Spread the rest of the batter on top, then finish with the remaining streusel.
Bake for 45–55 minutes, or until a toothpick inserted in the center comes out clean. If the streusel gets too dark, tent with foil.
(Optional Glaze)
Whisk together powdered sugar, dairy-free milk, and vanilla. Drizzle over the cooled cake before slicing.
