Preheat oven to 350°F (175°C) and prepare an 8x8 inch baking pan with non-stick parchment paper.
In a large bowl, whisk together the oat flour, protein powder, baking powder, baking soda, pumpkin pie spice, and salt.
In a separate bowl, combine the pumpkin puree, 1/2 cup Greek yogurt, maple syrup, eggs, and 1 teaspoon vanilla extract until homogenous.
Integrate the wet ingredients into the dry ingredients, stirring until just combined to maintain a light crumb.
Pour the batter into the pan and bake for 25-30 minutes, or until the internal temperature reaches 200°F or a toothpick comes out clean.
Allow the cake to cool completely on a wire rack to prevent the frosting from melting.
Prepare the frosting by beating the softened cream cheese, 1/4 cup Greek yogurt, powdered erythritol, and 1/2 teaspoon vanilla until smooth and aerated.
Spread the frosting evenly over the cooled cake surface and slice into 9 equal portions.