Preheat the oven to 180°C. Sift the flour and mix all the dough ingredients, then knead well until the mixture is homogenized and forms a soft dough.
Let the dough rest for half an hour. Place it in a shallow pan that has been greased with olive oil. Spread the dough with your fingers until it covers the entire surface of the pan.
Cover the dough with onion slices, then spread the tomatoes on top. Sprinkle with oregano and salt. Pour the remaining olive oil over everything and bake the ladenia at 180°C for 35-40 minutes. Serve warm or lukewarm.