In a large bowl, whisk together the oat flour, almond flour, flax seeds, hemp seeds, slivered almonds, baking powder, baking soda, pumpkin pie spice, and salt.
To a blender, add the soy milk, Greek yogurt, pumpkin puree, almond butter, maple syrup, vanilla extract, and apple cider vinegar.
Blend until smooth.
Pour the wet mixture into the dry ingredients and stir until just combined.
Spoon the batter into the muffin tin.
Top the muffins with pumpkin seeds or rolled oats, if desired.
Bake for 28-35 minutes, until a toothpick inserted in the center of the muffins comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.