Preheat your oven to 350°F.

Generously grease an 8x4-inch loaf pan with cooking spray.

In a large mixing bowl, combine the mashed bananas, melted butter, sugar, beaten egg, and vanilla extract, stirring well.

In a separate smaller bowl, whisk together the gluten-free flour, baking soda, baking powder, and salt. Add this dry mixture to the wet ingredients and stir until just combined; the batter may appear slightly lumpy due to the mashed bananas.

Pour the batter into the prepared loaf pan. Bake for 50 minutes to 1 hour, or until a tester inserted into the center comes out clean.

Allow the banana bread to cool on a wire rack for at least 15 minutes before carefully removing it from the pan. Cool completely before slicing and serving.