Preheat oven to 350 degrees Fahrenheit.
Grease 18 muffin cups with nonstick spray or line with paper liners.
In a medium bowl, combine flour, xanthan gum (if using), oats, baking soda, baking powder, cinnamon, pumpkin pie spice, and salt.
In a large bowl, beat together eggs and sugar.
Add the vanilla extract, pumpkin puree and oil. Beat well.
Stir in the flour mixture and mix together until just combined.
Mix in the chocolate chips.
Spoon into muffin cups.
Bake for 20-25 minutes or until the tops of the muffins spring back when touched. Cool in pan for 5 minutes and then finish cooling on a wire rack.