Sift the flour with the salt and sugar. Add the yeast, olive oil and water, then knead a dough. Place the dough in an oiled bowl, cover and leave in a warm place until it doubles in volume.
Oil 2 baking dishes. Heat the oven to 392°F (200°C). Cut the dough in 2 and roll it out.
Place them in the prepared baking dishes. Cover and leave them for 30 min. Then make holes with your finger in the dough and leave for another 20 min.
Cut the onions, pour them on top of the Focaccias, pour on olive oil and sprinkle with salt. Bake for 25 min.