Preheat oven to 400 degrees. Set aside a large baking sheet.
On a large piece of parchment paper or a large piece of aluminum foil coated with cooking spray, roll (or press with your fingers) the puff pastry sheet into a 12-inch square (it doesnt have to be perfect). Transfer pastry, on the parchment or foil, to the baking sheet.
Using a fork, prick the dough in a line around the dough, about 1-inch in from the edge, to create a border.
Spread the pesto evenly inside the border, leaving the 1-inch border plain. Top with the tomatoes and mozzarella.
Bake for 15 to 20 minutes, until the crust is golden.