Fill a medium-size bowl with cold water. Peel the potatoes and give them a quick rinse under running water. Shred them with a mandoline or a julienne peeler along the length of the potato. You want the shreds to be like long, thin matchsticks. Submerge them immediately in the bowl of water to rinse off excess surface starch. Usually 30 minutes is a good amount of time to soak them, but I have been known to soak them overnight in the refrigerator.
Cut the bell pepper in half lengthwise and discard the stem, seeds, and ribs. Thinly cut the pepper halves lengthwise into matchstick-like shreds. Ideally they should be the same thickness as the potato shreds.
Lay out a clean cotton kitchen towel or several layers of paper towels on the counter, for drying the potatoes. Drain the potatoes in a colander and give them a quick rinse under cold running water. Give the colander a few shakes to rid the shreds of excess water. Spread the shreds out on the towel and pat them completely dry.
Heat 2 tablespoons oil in a wok or large skillet over medium-high heat. Once the oil appears to shimmer, drop in 2 of the chiles and stir them around until they blacken and smell smoky, 5 to 10 seconds. Add half of the potatoes and half of the bell pepper to the smoky oil. Stir-fry them vigorously, without stopping, to briefly cook the shreds but still make sure they maintain their toothsome quality (*Footnote 7), 2 to 3 minutes. Scrape everything into a serving bowl. Wipe out the pan with paper towels before you repeat with the remaining oil, chiles, potatoes, and bell pepper. (*Footnote 8)
Add them to the batch in the bowl, stir in the vinegar, sesame oil, and salt, and serve immediately. (*Footnote 9)