Put the oranges in a small pot and cover them well with tap water. Put the pot on the fire and let the water boil. Lower the heat and simmer for 30-40 minutes or until the oranges are soft. Take the oranges out of the water and let them cool. Cut the oranges in half, remove the seeds, put them in a blender and grind.
Prepare the syrup: In a saucepan, put the sugar, water, orange juice, cinnamon, and orange peel. Stir, let it simmer and lower the heat. Boil for 7-8 minutes. Let the syrup cool.
For the orange pie: Preheat the oven to 180°C. In a bowl, put the semolina, baking powder, mastic powder, and mix.
In the bowl of the mixer, put the sugar, the oil, and beat for 5 minutes, to dissolve the sugar and make it creamy. Add the eggs one by one, waiting for each one to be incorporated into the mixture before adding the next. Lower the speed of the mixer and add the ground oranges and the semolina mixture spoon by spoon.
Put the mixture in a rectangular pan with dimensions of 23x28 cm and sprinkle its surface with the coarsely ground almonds.
Bake in the preheated oven for 40 minutes. Take the cake out of the oven and slowly add the cold syrup. First at the edges and then in the center. Leave aside to absorb the syrup. Serve with mastic ice cream.