Preheat oven to 350 degrees, and line an 8x8 baking pan with parchment paper, then grease. Place all ingredients for the cinnamon crumb topping in a food processor and pulse until crumbly.
1/3 cup gluten free all-purpose flour, 1/3 cup brown sugar, 1 teaspoon cinnamon, 3 tbsp butter
In a large mixing bowl, stir together flour, sugar, pumpkin pie spice, baking soda, baking powder, and salt.
1¼ cup gluten free all-purpose flour, 3/4 cup sugar, 2 tsp pumpkin pie spice, 1 tsp baking soda, 1 tsp baking powder, 1/2 tsp sea salt
In a separate bowl, whisk together egg, yogurt, pumpkin, butter, and vanilla extract.
1 egg, 1/2 cup plain Greek yogurt, 1 cup pumpkin puree, 1/4 cup butter, 2 tsp vanilla extract
Pour wet ingredients over dry ingredients, stir until just combined.
Transfer the batter into the prepared baking pan and spread out evenly.
Sprinkle the top with the cinnamon crumb topping mixture, then bake for 36-40 minutes, until a toothpick inserted in the center comes out clean.
Cool for 15 minutes then remove from the pan and transfer to a wire rack. If you want, you can sprinkle with powdered sugar. Slice into squares and enjoy warm or at room temperature.
OPTIONAL: powdered sugar