Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius) and line an 8x8 inch baking pan with parchment paper.

In a large mixing bowl, whisk together the Greek yogurt, egg, and vanilla extract until the mixture is smooth.

Add the monk fruit sweetener to the wet mixture and whisk until well incorporated.

In a separate bowl, sift together the cocoa powder, oat flour, protein powder, baking powder, and salt.

Gradually fold the dry ingredients into the wet ingredients using a spatula until just combined, ensuring no large clumps of protein powder remain.

Fold in the sugar-free chocolate chips.

Pour the batter into the prepared baking pan and smooth the top with a spatula.

Bake for 22 to 25 minutes, or until a toothpick inserted into the center comes out with only a few moist crumbs.

Remove from the oven and allow the brownies to cool completely in the pan for at least 30 minutes to set the structure before slicing into 9 even squares.