1. Heat a cast iron skillet or grill pan over medium-high heat. Add the chiles in a single layer, not too close together. (As shown in the post. If you have a lot, best to do them in batches.)
2. Let the chiles roast until they are browned on the bottom, which will take about 10 minutes. Use tongs to turn the chiles, roasting them on all sides, until the feel cooked through. Remove each chile as it’s done and put it in a paper bag and close the top, or a heatproof bowl, covering it with a plate to make a lid. (The steam will help loosen the skins as they cool.)
3. Once the chiles are cool enough to handle, either completely cut them all the way through in half, vertically, or slit them open so they lie flat. With a paring knife, scrape away the seeds, then turn the chiles over and pull away the skin.
(With some peppers, you may be able to just pull the skin off right away, while others may be a bit more stubborn. You can leave tiny bits on, unless you feel you must trim them away with a paring knife.)
4. Quickly dip the roasted chiles in a bowl of water or run them under the faucet, if you wish, to remove any stray seeds and pat them dry. Lay them in a serving dish and drizzle them with a generous amount of olive oil, and sprinkle them with salt and pepper, finishing with a scattering of chopped or picked parsley leaves.