Position a rack in the center of the oven and heat the oven to 350 degrees F.
Rinse the capers well. If using salt-packed capers, soak them in warm water for at least 5 minutes. (They should taste capery rather than salty; if not, continue soaking for a little longer.) Drain the capers and, unless they're very small, coarsely chop them. Combine the capers, cabbage, red onion, parsley, chives, oregano, and chiles (if using). Add the vinegar and 1/4 teaspoon salt, toss well, and let sit at room temperature for at least 30 minutes. Toss again and season to taste with more salt or chile.
Meanwhile, put the pork in a small baking dish . (If you have any juices left, scrape them into the dish, skimming and discarding as much of the congealed fat as possible.) Cover with foil and bake the pork until warmed through, 10 to 15 minutes. Remove the pork from the oven, position a rack 6 inches from the broiler, and heat the broiler to high.
Cut the baguette crosswise into 4 equal portions (each 5 to 6 inches long) and then slice each piece horizontally so that it opens like a book. Just before serving, put the baguette pieces on a baking sheet , opening each as much as possible, and toast very lightly under the broiler, 2 to 3 minutes. Divide the pork into 4 equal portions and mound on the bottom half of each piece of baguette. Drizzle any pan juices over the pork and then pile on the cabbage slaw. Drizzle the olive oil over the slaw. If any vinegar has collected on the bottom of the slaw bowl, distribute it among the sandwiches, and serve.
Slow-Roasted Pork Shoulder:
Combine 2 tablespoons salt and 2 teaspoons pepper in a small bowl and rub the mixture all over the pork. Put the pork, fat side up, in a large roasting pan (about 12x16x3 inches). Cover and refrigerate overnight or for up to 3 days.
Remove the pork from the refrigerator and let sit at room temperature for 1 to 1-1/2 hours before cooking.
Position a rack in the center of the oven and heat the oven to 300 degrees F. Uncover the pork and roast until tender everywhere but the very center when pierced with a fork, 4 to 4-1/2 hours. Add the onion, carrots, garlic, wine, and 1 cup water to the roasting pan and continue to roast, stirring the vegetables occasionally, until the pork is completely tender, about 1 hour more.
Remove the roast from the oven and raise the oven temperature to 375 degrees F. Using tongs, separate the pork into 8 to 10 large, rustic chunks and spread out on the pan. If most of the liquid has evaporated, add a splash more water to the pan to create a little more juice. (It shouldn't be soupy.) Return the pork to the oven and continue to roast until nicely browned on the newly exposed surfaces, about 15 minutes. Remove the pan from the oven, transfer the meat and vegetables to a serving platter , and tent loosely with foil. Let rest for 20 minutes. Skim the excess fat from the juices and serve the juices with the vegetables and meat.
