Preheat oven to 350F, spray 8x8 baking pan with non-stick cooking spray, and set aside.
In a large mixing bowl, combine flours, granulated sweetener, baking powder, baking soda, and salt. Whisk until thoroughly combined.
Add in mashed banana, water, and lemon juice, and stir.
Add blueberries, and stir again.
Pour batter into baking pan, and bake for 30 minutes.
Notes
*Or other granulated sweetener of choice, equivalent to 3/4 cup sugar**Note: One reader commented that she need more liquid to make the dough - if that is the case for you, add more water one tablespoon at a time.