Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or coat with non-stick spray.
In a large mixing bowl, whisk together the oat flour, protein powder, baking powder, baking soda, pumpkin pie spice, and salt until evenly distributed.
In a separate medium bowl, combine the pumpkin puree, Greek yogurt, eggs, maple syrup, and vanilla extract, whisking until smooth.
Gradually pour the wet ingredients into the dry ingredients, stirring with a spatula until just combined. Do not overmix.
Divide the batter evenly among the 12 muffin cups, filling each approximately three-quarters full.
Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove from the oven and allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.