Preheat the oven to 200 degrees Celsius (392 degrees Fahrenheit).
Mix together sugar, baking powder, vanilla powder, salt, flour, lemon zest, and oats in a bowl.
Add eggs, butter, and marzipan to the bowl and mix with a hand mixer into a crumble mixture.
Take 3/4 of the crumble dough and spread it in a small ovenproof dish lined with parchment paper. Press it well into the bottom so the dough becomes firm and cohesive.
Spread the fruit filling on the base and sprinkle the remaining crumble on top.
Bake for 30 minutes in the oven at 200 degrees Celsius (392 degrees Fahrenheit). The cake should be golden on top. When the cake has cooled, the bars can be cut out.