Pre heat oven to 210c, and line a rimmed baking tray with baking paper and set aside.
Take your pastry sheet out of the freezer to thaw while you prepare the rest of the ingredients.
Using a meat mallet (or something else heavy!) lightly pound out the thicker end of each breast, just to make them the same thickness all over.
Place breasts on to the prepared tray, then spread 2 tsp of basil pesto onto each breast.
Place overlapping slices of mozzarella on top of the pesto, then roughly spread another 2 tsp of basil pesto on top of mozzarella.
Place overlapping slices of tomato on top of final pesto layer and sprinkle with salt and pepper, then set aside briefly.
With a sharp knife, divide the sheet of puff pastry into quarters. Then cut each individual quarter into 4 even strips.
Place 4 strips over each layered chicken breast leaving space between each strip, and lightly tuck the ends of the pastry under the chicken. It's ok to stretch it slightly if you need to. See video.
Bake for 20 mins, or until chicken is cooked through.