Preheat the oven to 350°F. Line an 8x8-inch baking dish with parchment paper and set aside.
In a small bowl, combine 1 tablespoon ground flax seed (or chia seeds) with 3 tablespoons water. Whisk until smooth. Set aside to thicken for at least 10-minutes.
In the bowl of a food processor (or a blender), combine the wet ingredients (flax egg, drained and rinsed garbanzo beans, pure maple syrup, tahini and water or milk). Blend until smooth.
To the food processor, add the dry ingredients (cacao powder, protein powder, baking soda and salt). Blend again until a thick batter forms. Scrape down the sides and blend once more to assure everything is evenly combined. Add the chocolate chips (reserve a handful for topping later) and pulse a few times.
Transfer the batter to the lined baking dish. Use a spatula to spread to the sides. The batter will be thick and somewhat difficult to spread but just do the best you can. Like I said, they aren't going to be pretty. Place the remaining chocolate chips on top and press down into the batter.
Bake in the preheated oven for 25-30 minutes. Set aside to cool completely before slicing into 16 pieces, and enjoy!
Notes
Nutrition Facts are for 1/16th of the recipe. They are an estimate and will vary depending on specific ingredients/brands you choose.