Preheat the oven to 350°F. Line a muffin pan with liners or use a silicone muffin pan.
In a large bowl, combine the ground flaxseed and water. Let sit for five minutes, or until thickened.
Add the pumpkin purée, milk, coconut sugar and coconut oil. Mix until smooth.
Add the oat flour, cocoa powder, pumpkin pie spice, baking powder, protein powder, baking soda and salt. Stir until combined.
Fold in the chocolate chips, if using.
Fill each muffin cup approximately ¾ full.
Bake for 22–25 minutes, or until cooked through.