Preheat oven: Preheat your oven to 350°F (175°C). Grease an 8x8 inch baking pan.
Combine wet ingredients: In a large bowl, whisk together the brown sugar, applesauce, oat milk, and mashed banana until well combined.
Add dry ingredients: In a separate bowl, combine the gluten-free flour, protein powder, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in chocolate chips: Gently fold in the semi-sweet chocolate chips.
Pour into pan: Pour the batter into the prepared baking pan.
Bake: Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Cool and serve: Let cool completely before cutting into squares.