Peel the banana and slice it thinly.
Dissolve coffee in hot water and let it cool.
Mix mascarpone cheese and Greek yogurt well in a bowl.
Layer banana slices at the bottom of a bowl or cup.
Place castella (or sponge cake) soaked in cooled coffee on top.
Add the cheese-yogurt cream and create layers.
Sift cocoa powder on top.
Let it set in the refrigerator for 1 to 2 hours before serving.