While the dough is resting prepare the tomato topping.
Preheat the oven to 375 degrees. Remove the stems from the tomatoes and slice in half lengthwise. If the tomatoes are extremely watery, gently squeeze out some of the seeds. A little juice is good you just don't want them watery. Lay the tomatoes in a single layer on the baking sheet, cut side up, and drizzle with olive oil. Add the garlic and toss gently to cover. Sprinkle the tomatoes with the thyme leaves, salt and pepper. Roast for 30 - 40 minutes depending on the size of the tomatoes.
Remove the tomatoes and garlic from the oven and place in a medium bowl. Using the back of a fork, gently crush the tomatoes and garlic together leaving some pieces chunky. Pierce the tomatoes before smashing or they will spit juice in your face - just saying. Set aside.
When ready to cook the pizza place the cast iron skillet on the stove top and heat (ungreased) on medium heat for at least 10-15 minutes. If the pan begins to smoke, reduce the heat. Preheat the broiler to LO with the oven rack in the center.
Turn the dough out onto a lightly floured work surface. Divide the dough into two or three pieces (depending the size of your skillet) and cover the pieces set aside to work with later. Shape the dough into a ball and then flatten into a disk. Roll the dough into a 10-inch circle (for a 9 inch skillet) using a rolling pin. If the dough snaps back and doesn’t hold it’s shape, let it rest a few minutes then try again. Transfer the dough to the pizza peel or rimless baking sheet dusted with cornmeal.
Spread half the diced mozzarella on the pizza dough. Spoon half the tomatoes and garlic on the prepared pizza leaving some cheese uncovered.
Slide the dough into the hot skillet on the stove top. Immediately place in the middle of the oven with the broiler on LO with the oven door propped open. Broil for about 5 minutes. Once the cheese melts you can move the skillet up to a higher rack if needed to brown the dough. Watch it carefully as it can burn in a few seconds.
Remove from the oven and cool slightly. Garnish with fresh basil leaves and a dash of crushed red pepper if desired. Serve immediately.