Heat a dry frying pan and toast the walnuts. Remove from the pan and set aside. Sprinkle the sugar into the pan and melt over a high heat. Pour in the balsamic vinegar. Add the figs and cook for 1-2 minutes then remove the pan from the heat.
Divide the watercress between 4 plates and spoon over the figs with the juices. Sprinkle with the reserved walnuts and the shavings of Grana Padano. Drizzle with the olive oil and serve immediately.