Preheat your oven to 350°F (175°C) and line an 8x8-inch baking dish with parchment paper, allowing some overhang for easy removal later.
In a large mixing bowl, whisk together the cocoa powder, zero-calorie sweetener, whole wheat flour, baking powder, and salt until well combined.
In a separate bowl, mix the Greek yogurt, eggs, and vanilla extract until smooth and creamy.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix the batter.
If using, fold in the dark chocolate chips for an extra layer of richness.
Spread the brownie batter evenly in the prepared baking dish and smooth the top with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan before lifting them out using the parchment paper. Cut into squares and enjoy!