Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius) and grease an 8x8 inch baking pan.
Place rinsed black beans, egg whites, liquid sweetener, and vanilla extract into a high-speed blender or food processor.
Process until the mixture is completely smooth and no bean skins are visible.
Add protein powder, cocoa powder, baking powder, and salt to the blender.
Pulse until just combined, adding water or almond milk 1 tablespoon at a time if the batter is too thick to blend.
Fold in sugar-free chocolate chips by hand.
Pour the batter into the prepared baking pan and smooth the top with a spatula.
Bake for 20 to 25 minutes until the edges are firm and a toothpick inserted into the center comes out mostly clean.
Allow to cool completely in the pan for at least 30 minutes before slicing to allow the structure to set.