Heat oven to 200c/fan 180c/gas 6. Unroll the pastry onto a flat baking sheet and, using a sharp knife, score a rectangle two finger-widths from the edge. Fork the pastry all over the inside of the marked edge. Scatter the cheese, olives and tomatoes over the centre of the tart, then season to taste.
Bake for 20-25 mins until pastry is crisp and risen, tomatoes are soft and the cheese is golden. Drizzle over the pesto and cut the tart into slices to serve. Great with a green salad.