Preheat oven to 175°C (347°F) with convection/fan setting.
In a bowl, combine oatmeal, protein powder, egg whites, muesli, raisins or cranberries, and milk. Mix thoroughly until the batter is thick and viscous, adjusting the milk amount as needed.
Line a baking sheet with baking paper.
Spread the batter evenly onto the prepared baking sheet.
Bake for 10-15 minutes until the top is golden and set.
Cool for 5-10 minutes, then cut into bars or strips.