In a bowl, combine oat flakes, cocoa, and sweetener. Mix. Add peanut butter and a bit of boiling water (about 2-3 tablespoons – it's best to add one tablespoon at a time and observe the consistency of the mixture). Thoroughly crush and mix with a spoon. The mass should be compact and only slightly sticky. If necessary, add a little more water and mix and crush again.

Divide the mixture into 2 parts and shape the bars with moistened hands.

Place the bars in a sealed container or wrap in cling film. Put them in the refrigerator to cool and harden (minimum several hours, preferably overnight).