Use a rolling pin to roll the cold dough on a lightly floured surface until you have a round of about 14 inches in diameter.
Transfer it carefully to a piece of parchment paper placed on a baking sheet.
Spoon the cheese mixture on the center of the rolled pie dough and spread with the back of a spoon, making a circle of about 9 or 10 inches and leaving an edge of several inches (2-inch border at least) of dough without filling.
Cut fresh tomatoes into slices and blot with paper towels to avoid adding too much liquid to the galette. Place the tomatoes on top of the cheese in whatever pattern you want to, just don't mound them too high.
Lift the edge of the dough and fold it inward, covering some of the filling. Keep doing that with all of the dough until you have a circular tart with an exposed center.
If you feel the pie is too warm or starting to look shiny, you may want to pop it in the freezer for 5-10 minutes, no more, before going into the oven. A cold dough helps prevent a soggy crust.
Sprinkle with salt and pepper if desired, drizzle with olive oil and bake for about 40 minutes, or until it's golden and dry and the filling is bubbly and slightly burnt.
Let cool slightly and eat warm. Or let cool completely and eat at room temperature.
Refrigerate leftovers, well covered in plastic wrap or in an airtight container.