Tip the sugar into a bowl and pour in 350ml warm water. Stir well to dissolve the sugar, then mix in the yeast. Add the flour, salt, 2 tbsp of the olive oil and the chocolate. Stir well to bring together into a ball and tip out onto a lightly floured work surface and knead for 5-10 mins until elastic, soft and less sticky. Transfer to a clean bowl, cover and set aside to rise in a warm place for 1-2 hrs, or until doubled in size.