Preheat oven to 350 degrees. Grease an 8x8 square metal cake pan and set aside.
Combine the flour, sugar, pumpkin pie spice, baking soda, salt and baking powder in medium bowl.
Whisk together the pumpkin, apple, oil, egg and vanilla in a separate, large bowl. Add dry ingredients to the wet, mixing just until moistened.
Batter will be very thick.
Spread the batter evenly into the prepared pan.
In a clean bowl, stir together the remaining flour, brown sugar and pecans. Add in the butter and stir until crumbly. Using your hands, crumble the streusel evenly atop the cake batter.
Bake the cake for 45 - 50 minutes, or until a cake tester inserted into the center of the cake comes out clean and the top of the cake springs back easily when pressed.
Allow to cool in the pan. Slice and serve.