Preheat a grill to medium and arrange a large cast-iron skillet on the grate. Add the bacon to the skillet and cook until crisp-tender, 5 to 7 minutes. Discard the fat and transfer the bacon to a paper-towel-lined plate to drain. Let cool, then finely chop.
Heat 1 tablespoon olive oil in the skillet. Add the onion, season with salt and pepper and cook, stirring, until golden, about 10 minutes.
Meanwhile, grease the grill and a large baking sheet with the remaining 1 tablespoon olive oil. Cut the pizza dough into quarters, form into 4 balls and place on the baking sheet. Flatten the dough balls by pressing with the heel of your hand to make four 4-inch rounds. Stretch out 2 rounds, holding each upright with your hands and working in a circular fashion, until they are 7 inches in diameter.
Lay 1 pizza round on each side of the greased grill, cover and cook until the dough bubbles on top and is golden underneath, about 3 minutes. Flip the pizzas and, working quickly, top each with one-quarter of the onion, cheese and bacon. Cover and cook for 2 minutes. Remove the pizzas from the heat, sprinkle with the thyme and top with the tomatoes. Repeat with the remaining 2 pizza rounds. Cut into wedges and serve.