Preheat oven to 350ºIn a large bowl, mix together flour, xanthan gum, salt, baking soda, cinnamon, and brown sugar. Set aside.Mash banana (blend in a food processor if you have oneBeat in eggs, oil, and vanilla. (Pulse to combine if using the food processor)Shred zucchini and add to banana/egg/oil mixture.Pour wet ingredients over dry ingredients and mix until everything is combined. Use a rubber spatula to scrape flour up from the bottom and mix it in.Divide batter evenly between 18 greased muffin cups.Place the muffin pans in the center of the preheated oven, and bake, until the tops are golden brown and a toothpick inserted in the center of each loaf comes out clean (about 15-20 minutes).Remove from oven and allow to cool for ten minutes.Loosen edges with a butter knife, and remove to a wire cooling grid to finish cooling.Ideally, you would let it cool completely before serving, but if you’re like me, hot muffins and butter is just too tempting, so enjoy!