Preheat oven to 350°.
Spray 8x8 baking pan with cooking spray.
In a medium mixing bowl, whisk together all dry ingredients: rice flour, cocoa powder, baking powder, baking soda, and salt. In a separate bowl, mix together all wet ingredients: mashed banana, pumpkin puree, egg whites, and cake batter extract. *I use cake batter extract because I think it adds a great cakey flavor, but you can certainly use vanilla extract if that's what you prefer or have on hand. Whisk together wet and dry ingredients until well combined.
Pour batter into greased baking pan and spread evenly.
Bake for 28-30 minutes, until cooked through. You can check whether your cake is ready by sticking a toothpick into the center of the cake - as long as no wet batter sticks to the pick, your cake is ready.
Allow your cake to cool completely before frosting.