Prepare the cake tin by either lightly greasing it or lining it with parchment paper (see recipe notes for instructions). Sprinkle some coconut sugar over the cake tin and arrange the apples in a circular pattern, starting from the outside and working in. Repeat, creating layers, until you have used up all the apples.
Preheat the oven to 180 degrees C/350 degrees F.
Meanwhile, whip the aquafaba using a handheld mixer until stiff peaks form. This usually takes around 10 minutes, so be patient with it.
Once stiff peaks form, continue whisking and gradually add in the coconut sugar. Next add the lemon juice and cinnamon. Once they are well-combined, stop the mixer and gradually add the flour, mixing using a spatula or a spoon.
Pour the batter into the cake tin and bake in the preheated oven for 20 minutes, until golden brown. When the cake cools down fully, flip it by holding the bottom of the cake while wearing oven gloves, placing a plate or a cake stand on top of it and flipping it over carefully.
To easily line a circular cake tin, place it on a sheet of parchment paper and draw with a pen around the circumference. Cut around the outline and place the circle at the bottom of the cake tin.