All you will need is puff pastry, mozzarella, fresh tomatoes, dried italian herbs, and a beaten egg.
You can use ready-made puff pastry, I use Jus-Rol pastry. Simply roll it out and cut into circles, or any shape, with a cookie cutter or something similar.
Brush the outsides of the circle with beaten egg, and place a slice of mozzarella in the middle, topped with a slice of tomato. Sprinkle with herbs and bake in the oven for around 10-15 mins on about gas mark 4 or 5 (180-200 degrees)
I made these to take to a buffet once, they were easy to re-heat in the oven and tasted delicious.