Mix all the solid ingredients together for the dough. Add water until a viscous batter is formed (a shot from the tap). Pour the dough onto a baking sheet lined with baking paper and spread it on. If you want to use a pan so that it looks more like a cake and is taller, take this one. With the baking paper itself, it looks more like a pizza afterwards. Cut the apple into fairly thin slices and use them to cover the dough. Put the dough in the oven for 20 minutes.
For the crumbles, mix the oat flakes with the peanut butter until you get small crumbles. After the 20 minute baking time, put the crumble on the cake and bake again for 8-10 minutes. When the crumble is brown, take out the cake and eat it either cold or warm.
I really like to eat it for breakfast - it looks like a lot, but in principle it`s not that much.