Fold out the unthawed puff pastry on to parchment paper. Lightly roll it out to smooth out the creases. Using a knife, score a frame around the edge of the pastry about 1/2 inch away from the edge.
Next, take a fork and prick the inside of the frame several times - this will keep the inside from rising when it bakes.
Combine the pesto & mustard and slather the inside of the frame with this mixture. Sprinkle with grated gouda cheese and top with the tomatoes. Keeping all the ingredients inside the "frame" of the pastry.
Sprinkle the capers around the tart and top with the goat cheese. Season lightly with salt and freshly cracked black pepper.