Bring oats, rice, barley, cinnamon, vanilla, salt and 5 cups water to the boil in a medium saucepan over high heat. Reduce heat to low and simmer, covered, stirring occasionally, for 40 minutes or until grains are tender and liquid has been absorbed.
Stir in milk and half the syrup, then cook for 2 minutes or until heated through.
Divide porridge among bowls. Top with yoghurt, nectarine, persimmon and hazelnuts. Sprinkle with extra cinnamon and serve drizzled with remaining syrup.