Preheat oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan.
In a large bowl, whisk together gluten-free flour, tapioca starch, sugar, baking powder, and salt.
In a separate bowl, whisk together milk, melted butter, and egg.
Add the wet ingredients to the dry ingredients and mix until just combined.
In a small bowl, combine brown sugar and cinnamon.
Pour half of the batter into the prepared loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter. Pour the remaining batter over the cinnamon sugar, and sprinkle with the remaining cinnamon sugar.
Bake for 35-40 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Notes
Store leftover bread in an airtight container at room temperature for up to 3 days.