Mix 1 tablespoon of the oil with the garlic, Parmesan and pesto. Slice the polenta horizontally into 2 thin slabs, then cut each in half to make 4 chunky slices. Cut each of the slices in half horizontally and use to sandwich the filling, making 4 sandwiches.
Arrange, slightly apart, in a shallow, ovenproof dish and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 15 minutes.
Meanwhile, mix the tomatoes in a bowl with the red onion, parsley, chives, olives, pine nuts and a little salt. Pile on top of the polenta and return to the oven for a further 15 minutes.
Beat the remaining oil with the balsamic glaze. Transfer the polenta stacks to serving plates and drizzle with the dressing. Serve with a rocket salad.