Preheat the Oven: Preheat your oven to 350°F (175°C). Grease a loaf pan.
Prepare the Batter: In a large bowl, mix the mashed bananas and melted butter. Add the sugar, egg, and vanilla extract, and mix well. Stir in the baking soda and salt. Gradually add the gluten-free flour and mix until just combined.
Bake: Pour the batter into the prepared loaf pan. Bake for 60-65 minutes or until a toothpick inserted into the center comes out clean.
Cool and Serve: Allow the banana bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely. Slice and serve.