Grease a deep 22cm round cake pan. Line base and side with baking paper.
Combine flour, semolina, sugar, eggs, oil, rind and juice in a medium bowl. Beat with an electric mixer for 2 minutes, or until smooth. Spoon into prepared cake pan.
Cook in a moderate oven (180C) for about 50 to 55 minutes, or until a skewer comes out clean.
Meanwhile, to make syrup, place 1 cup of the sugar and water in a saucepan. Stir over a low heat until sugar is dissolved. Bring to boil. Add orange slices. Boil gently for 6 to 7 minutes, or until pith is tender. Using tongs, transfer orange to a plate. Discard syrup.
Place remaining sugar and juice in a clean saucepan. Stir over a low heat until sugar is dissolved. Bring to boil. Boil gently for 5 minutes.
Using a skewer, pierce holes all over cake in pan. Spoon hot syrup over hot cake. Stand for 30 minutes, then transfer to a plate.
Serve cake warm or cold topped with orange slices.