Heat the oil in a pan. Sauté the onion and garlic. Pour in the stock and bring to the boil. Stir in the polenta, reduce the heat, simmer over a low heat for approx. 4 mins., stirring constantly to form a thick paste. Transfer the polenta to the prepared tin.
Spread the pesto, tomatoes and mozzarella on top of the polenta.
Approx. 15 mins. in the centre of an oven preheated to 220°C. Remove from the oven.
Top the pizza with the olives and rocket, drizzle with oil.