Place in a heavy pot the water, the zest, the sugar and the olive oil. Bring to the boil. Remove from heat when the bubbles start.
Add the semolina and mix well with a wooden spoon. The mixture should be thick. Pour half of the semolina mixture into a pudding mold. Stir the cocoa into the remaining half, mixing well. Place the cocoa mixture on top of the white semolina mixture.
Let it cool for 2 to 3 hours at room temperature before serving. Enjoy it.