Beat the eggs with the sugar with a mixer. Add the oil and beat, then then add the water (soft drink).
Sift the flour with baking powder and add to the mixture. Stir well until you obtain a homogeneous mixture.
Optionally, divide the mixture in 2 - pour 1 into an oiled and floured cake form, add the cocoa to the other and mix. Pour the brown mixture on top of the other one.
Bake in a preheated 356°F (180 °C) oven.
Check to see if it's ready with a toothpick.
You can sprinkle with powdered sugar before serving.