Preheat the oven to 350°F/180°C. Line a muffin pan with paper liners and lightly spray with cooking spray. Blend the rolled oats until fine and flour-like. In a large bowl, whisk together the oat flour, protein powder, baking soda, baking powder, salt, and pumpkin pie spice and/or cinnamon.
In a separate bowl, whisk the pumpkin purée, eggs, sugar, milk, and vanilla extract until smooth.
Add wet ingredients to dry and stir until just combined.
Divide batter evenly among the 10 muffin cups, filling each to the top. Mix pumpkin seeds, sugar, and pumpkin pie spice and/or cinnamon; sprinkle over muffins, gently pressing seeds into the batter.
Bake 18–20 minutes, until a toothpick inserted into the center comes out clean.
Cool in the pan a few minutes, then transfer to a wire rack to cool completely.