Preheat oven to 180°C. Line a large baking tray with baking paper.
Boil the water, then add the butter. When the butter is melted stir in the oatmeal.
Let it stand for a while, until the oatmeal soaks up the water and a dough forms.
Using your fingers, form small dumplings and place them on the baking sheet. Flatten them your fingers or a spoon (to about half a cm thick). It doesn't matter if their shape is irregular.
Bake for about 25 minutes until lightly browned.
Move them to a wire rack to cool completely.
When cooled you can grind them into rough or smooth crumbs.