Pre-heat oven to 220C/fan 200C/gas 7. Cut the pastry into 4 rounds with an 11cm (approx) cutter. Using a sharp knife, score a circle about 1cm in from the edge of each round.
Put the pastry rounds on a baking sheet, brush with egg and prick the bases with a fork. Spread each with tapenade or pesto, then arrange the sliced tomatoes on top and finish each with a couple of slices of mozzarella. Drizzle with a little olive oil, season and sprinkle with fresh thyme.
Bake for 15-20 mins until the pastry is golden and the base is cooked. Remove the tarts from the oven and transfer to plates. Top each tart with a few olives and serve with a rocket salad or top with a few rocket leaves.