Make the pizza base dough according to the packet instructions. Divide into 2 pieces and roll out each piece on a lightly floured work surface to an oval shape. Scatter a little polenta over 2 baking sheets, then place the bases on the sheets, cover and leave to rise for 15 minutes.
Place the onion, garlic, courgettes, olives and oil in a bowl and gently toss together, then season well. Scatter the mixture over the bases and drizzle over a little extra oil. Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 15–20 minutes until crisp. Scatter over the parsley and serve.