Preheat the oven to 350 F. Line 13 x 18 sheet pan or two 9 x 13 Inc pans with parchment paper.
In medium dish combine flour, granulated sugar, light brown sugar, baking soda and salt. Set aside.
In a smaller dish combine eggs, Greek yogurt and vanilla. Set aside.
In a big saucepan put butter, cocoa and water and bring to boil, at medium heat, stirring from time to time. Remove from heat.
Add dry ingredients in the saucepan. Whisk until well combined.
Add eggs and Greek yogurt mixture and whisk until combined. Put the batter in the sheet pan and bake for 20-22 min or until the edges of the cake are coming away from the sides of the pan.
Take out of the oven and let cool for 10 minutes.
TO MAKE THE CHOCOLATE FROSTING:
In a big saucepan combine butter and cocoa and stir at medium heat, until well combined. Bring to boil, stirring from time to time.
Remove from heat, add milk and vanilla and whisk. Whisk in powdered sugar.
Add ½ of the pecans and stir. Pour warm frosting and spread over the warm cake.
Sprinkle with the rest of the pecans.
Notes
Let the cake cool and frosting to form before serving.