Position a rack in the center of the oven and heat the oven to 450°F.
Cook the bacon in a 12-inch cast-iron skillet over medium heat, flipping occasionally, until crisp, 5 to 8 minutes. Drain on a plate lined with paper towels. Pour the bacon fat from the skillet into a small heatproof bowl, leaving a slick of fat in the skillet; you’ll need 4 tsp. reserved fat. (If you don’t have enough, make up the difference with extra-virgin olive oil.) Raise the heat under the skillet to medium high.
Sprinkle the cut sides of the peaches evenly with the sugar and a tiny pinch each of salt and pepper. Arrange the peaches in the skillet cut side down and tuck the herbs around them. Tear the bacon slices in quarters and tuck the pieces around the peaches. Drizzle 2 tsp. of the reserved bacon fat evenly over the peaches and let them cook undisturbed until the cut sides begin to brown, about 5 minutes.
Sprinkle the uncut sides of the peaches with a tiny pinch of salt, then transfer the skillet to the oven and roast until the peaches are just tender, about 10 minutes.
Flip the peaches, drizzle with 2 tsp. more of the reserved bacon fat, and continue to roast until they’re tender but not falling apart, about 5 minutes more. Enjoy the bacon as a cook’s treat, or save it for another use; discard the herbs. Let the peaches cool slightly before serving.
You can make the peaches up to 2 days ahead and refrigerate them in an airtight container. To reheat, arrange the peaches on a microwave-safe dish, cover loosely with a paper towel, and heat on high for about 1 minute.