Heat oven to 375° F. Unfold the sheet of puff-pastry dough on a lightly floured surface and roll to 1/4 inch thick. Transfer the dough to a baking sheet.
In a medium bowl, combine the tomatoes, garlic, thyme leaves, oil, vinegar (if using), salt, and pepper.
Using a slotted spoon, transfer the tomato mixture to the pastry, overlapping the tomatoes slightly if necessary, leaving a 1/2-inch border.
Crumble the goat cheese over the top. Bake until the dough is puffed and golden brown, 15 to 20 minutes. Let cool for a couple of minutes before cutting into pieces.