Preheat oven to 350°F (175°C)
Add Greek yogurt to a mixing bowl
Crack in the eggs
Add cocoa powder and sweetener if using
Whisk until the batter becomes smooth
Pour the batter into a lined baking pan
Bake for 30 to 35 minutes until set
Let cool completely
Chill in the refrigerator for at least 2 hours
Slice and serve cold
