Preheat the oven to 350°F. Grease an 8”x8 square pan with nonstick cooking spray and line with parchment paper, leaving an overhang for easy removal once baked.
In a large mixing bowl, whisk together the 2 cups Bob’s Red Mill Gluten Free 1 to 1 Baking Flour , ½ cup dark brown sugar, 1 tsp baking powder, 1 tsp baking soda , 2 ½ tsp ground cinnamon , 2 tsp ground ginger, ⅛ tsp ground nutmeg ⅛ tsp ground allspice, and ½ tsp Kosher salt.
Add the 1 15-ounce can pure pumpkin puree, 2 large eggs, ¼ cup oat milk, ¼ cup unsulfured blackstrap molasses and ¼ cup avocado oil to the dry ingredients and whisk together until a smooth batter forms, about 1 minute. Use a rubber spatula to fold everything together to ensure there is no flour left at the bottom of the bowl. The batter will look very thick and spreadable.
Transfer the batter into the prepared pan and smooth into an even layer.
Bake in the center rack of the oven for 36-38 minutes or until a toothpick inserted into the center comes out clean.
Transfer the pan to a wire rack to cool for 20 minutes before lifting up the parchment paper to transfer the cake onto the cooling rack. Let cool fully for 1 hour before slicing and serving.