Place the whole unpeeled orange and whole lemon into a saucepan. Cover with water and boil for one hour. Keep water topped up if needed to ensure that they remain covered. Once done, remove from the water and allow to cool completely.
Pre-heat oven to 300°F. Grease and flour a 9-inch cake pan.
Cut the cooked fruit open and remove any seeds. Place the fruit into a food processor and process until smooth. Add the margarine and sugar to orange and lemon mixture. Process on high until light and fluffy. Add the chia eggs. Process until well mixed well.
Spoon the mixture into a large mixing bowl. Add in the ground almonds and cornmeal. Stir together until well mixed.
Pour the mixture into the cake pan.
Bake for one hour turning halfway through the baking. When removing cake should be golden brown, well risen and firm to the touch. You can also use a tester in the center of the cake to insure it is done.
While baking, make the candied orange and lemon slices. Instructions are below.
Remove cake from oven. Let cool slightly in the pan for 5 minutes. Then turn onto a cake plate.
Warm the marmalade if needed to make a spreadable consistency. Spread it on top of the cake, covering it.
Add candied oranges and lemons as decorations if desired.
Making candied orange and lemon slices: Slice an orange and lemon uniformly and set aside. Slices should be 1/4-1/2 inch in thickness.
Place sugar and water into a medium size deep sauce pan. Bring to a boil. Add the fruit slices and let boil for 30 minutes to 1 hour.
Remove from heat and place on a baking rack to remove excess syrup.
Transfer the slices to a lined or lightly greased baking tray.
Bake at 300 degree for 30 minutes. Check them to insure they don't burn.
Remove the fruit slices from oven, and let them cool and harden on a baking rack.