Preheat the oven to 350℉. Line a 9x5" laof pan with unbleached parchment paper or generously oil the pan with coconut oil.
In a large mixing bowl, combine the mashed banana, oil, maple syrup, and eggs. Stir until combined.
Add the gluten-free flour, baking soda, baking powder, sugar, salt, and cinnamon. Stir until the batter is smooth. Fold in the pieces of chopped chocolate bar.
Pour the batter into the loaf pan. Use your spatula to smooth the batter into the pan.
Bake for 45-55 minutes. The top of the loaf should be risen nicely and browned. It should be set when pressed gently or when a cake tester is inserted in the center of the loaf.
Allow the loaf to cool in the pan for 10-15 minutes before removing from the loaf pan. Slice the banana bread while it is still warm to get pretty banana bread slices!
Store leftover, cooled banana bread in an airtight container at room temperature for up to 2 days or in the fridge for up to 5 days.