Preheat oven to 350° Fahrenheit and line a 12 cup muffin pan with muffin liners.
Mix together the pumpkin puree, oil, maple syrup, milk, eggs, and vanilla extract in a large bowl.
Add in the oat flour, pumpkin pie spice, baking powder, and baking soda and mix until everything is fully combined.
Scoop ¼ cup of muffin batter into each muffin liner, then sprinkle with either chocolate chips, pumpkin seeds, chopped nuts, or leave plain. Bake the muffins for 22-25 minutes, or until a toothpick inserted down the center of a muffin comes out clean.
Remove the muffins from the oven and transfer them to a wire cooling rack to cool completely before serving or storing.