Preheat oven to 350°F (175°C). Grease a muffin tin or line with muffin liners.
In a large bowl, mash the bananas. Add the melted butter, sugar, beaten egg, and vanilla extract. Mix well.
In another bowl, whisk together the gluten-free flour, baking soda, and salt. Gradually add the dry ingredients to the banana mixture, mixing until just combined.
Fold in the chocolate chips.
Divide the batter evenly among the muffin cups.
Bake for 20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.