Preheat oven to 325 degrees F. Prepare a 9" x 5" loaf pan lightly coated with cooking spray and line with parchment paper.

In a small bowl, sift together the gluten free flour, guar gum (omit if in blend), baking soda, salt, and ground cinnamon and set aside. In a stand mixer, beat the butter until smooth. Add the brown sugar until combined. Add one egg at a time, beating after each. Mix in the yogurt. Add the flour mixture and combine until it is just mixed. Add the mashed bananas and nuts (optional) and stir until combined.

Pour into prepared loaf pan. Sprinkle the top with raw sugar if desired. Bake for 50-55 minutes, checking around 40 minutes in to make sure it isn't over-browning (if it is, tent with aluminum foil), or until toothpick comes out clean. Allow to cool slightly before removing from pan.