Lightly oil a 25cm (10 inch) shallow round cake tin or pizza pan. Place the flour, salt and yeast in the Kenwood Bowl. Using the Dough Hook on minimum speed, gradually mix in the lukewarm water and olive oil to form a soft dough.
Knead for 1 minute on minimum and 4 minutes on speed 1, until smooth and elastic. Remove the Kenwood Bowl, cover with lightly oiled clear film and leave to rise in a warm place for about 1 hour, or until the dough has doubled in size.
Using the Dough Hook on minimum speed for 30-60 seconds knead the dough to knock back.
Transfer to a lightly floured surface and shape into a ball. Roll out into a 25cm (10 inch) circle and place in the prepared tin.
Cover with oiled clear film and leave to rise, in a warm place, for about 20 minutes or until almost doubled in size. Using your fingertips make deep dimples over the surface of the dough. Cover and leave to rise for about 10 minutes.
Meanwhile preheat the oven to 200°C/400°F/Gas Uncover and sprinkle over the sage leaves, red onion, salt and pepper.
Drizzle with the olive oil and bake for 20-25 minutes, or until golden. Cool on a wire rack and serve warm.