Preheat the oven to 180°C (350°F/Gas 4). Line two baking trays with baking paper.
Combine the oatmeal, baking powder, sugar and a pinch of salt in a large bowl. Make a well in the centre and add the melted butter and 125ml (4fl oz/½cup) hot water.
Using a flat-bladed knife, mix to form a dough. Gather the dough together and turn onto a surface lightly sprinkled with extra oatmeal, then press into a flattish round.
Roll the dough out to a thickness of 5mm (¼inch), sprinkling with extra oatmeal. Cut the dough into 6cm (2½inch) rounds with a biscuit cutter. Place on the baking trays, leaving room for spreading. Bake for 25 minutes, or until golden. Cool on the trays for 5 minutes, then transfer to a wire rack to cool completely. Store in an airtight container.