Preheat oven to 350 degrees F.
In a small bowl, mix together the chia seeds and lukewarm water. Set aside from 15 minutes. This will make the chia egg.
In a medium-sized bowl, mix the tahini, coconut sugar, maple syrup, oat milk and vanilla extract.
Once the chia egg is set after 15 minutes, stir it into the wet tahini mixture.
Add in the dry ingredients - cacao, baking powder and salt. Lastly, stir in the chocolate. Do not overmix the batter, but just enough to combine the ingredients thoroughly.
Pour the brownie batter into the prepared pan, or one lined with parchment paper. Use a greased rubber spatula to evenly spread the batter out.
Bake in the oven on the middle wire rack for 25 minutes, until a toothpick inserted in the center comes out clean.
Allow to cool for 10 minutes, then cut into 16 squares. Enjoy!