Preheat the oven to 180 °C top/bottom heat.
In a mixing bowl, mix flour, sugar, starch, cocoa, baking powder, vanilla, and salt. Add oil, oat milk, water, and vinegar. Using a whisk, quickly knead by hand to form a homogeneous dough.
Grease a 24 cm springform pan with some vegetable margarine and pour in the batter.
Bake on the middle shelf for 40-45 minutes. Then let cool completely in the mold.
Carefully remove the chocolate cake from the mold and place it on a cake plate.
Now cut the cake with a knife about 2 cm from the edge up to 1 cm above the bottom.
Then scoop out the chocolate cake with a spoon and crumble the scooped out into a bowl.
Halve the bananas and place them on the chocolate base.
Whip the cream with the whipped cream stiffener, sugar, and vanilla sugar, then fold in the chocolate shavings.
Spread the whipped cream over the bananas in a dome shape.
Finally spread the chocolate cake crumbs all over the cream dome and press down lightly.