Whisk the eggs with the sugar until you get a fluffy cream. Add the oil and in a little while, the sifted flour with the baking powder, the cold fruit tea and finally mix with the oats and lemon zest.
Pour half the cake mixture into a greased and lightly floured form. Distribute half the chokeberries on top, pour in the remaining mixture and top with the remaining chokeberries. Cut the apple into thin slices, roll them in some breadcrumbs and stuff them lightly at the top of the cake mixture.
Put the chokeberry cake to bake in a moderately heated 356°F (180 °C) oven for about 40 - 45 minutes, or until ready.