Soak the tomatoes in warm water to cover for about 20 minutes while you are making the dough. Drain the tomatoes, reserving the tomato water for later uses. Dry the tomatoes a little with a paper towel.
Heat 3 Tbsp olive oil in a large cast iron skillet until just smoking
Place the rolled-out dough round in the skillet and cook over med heat for about 3 minutes. While it is cooking, poke the bubbles that form with the tines of a fork to release the air and keep the dough flat.
When the bottom of the dough begins to crisp and brown (about 3 min.), use a pair of tongs to turn the dough over in the skillet
Place the tomatoes on top of the dough and the mozzarella on top of the tomatoes. Sprinkle with the garlic and the scallions.
Cover the skillet and turn the heat to med-low. Cook covered about 5 minutes, or until the cheese has melted.