Pour the oats to a trough and a large bowl. Blend beforehand. Add hot water and let it cool for 15-20 minutes.
After it cools, add cocoa to the oats (if any, add protein powder), mix well with a spoon.
Crush the banana with a fork and add honey. Then add it on the oats and mix well.
Add the walnuts.
Pour this mixture on baking paper, a silicone cup or a strech film and wrap it.
Wait in the deep freezer for 2 hours.
Finally, take your mosaic cake from the freezer and slice it and serve it.