Combine oatmeal, flour, salt, water, and yeast in a bowl and mix together.
Let the dough rise at room temperature for 1 hour (first fermentation).
Fold the dough, shape it, and place it in a basket for a second 1-hour rise.
Score the top of the dough and place it in a preheated oven at 230°C (446°F).
Bake for 25–30 minutes.
Transfer to a cooling rack and let it cool completely.