1: Soak the cloth in the wine in a large bowl. Wring it out and arrange the cloth on your work surface on the diagonal (like a diamond), so that one corner points towards you. Spread half the salt in the center of the cloth, then sprinkle with half the oregano. Lay thee tenderloin in the center of the salt and season with the remaining oregano. Top with the remainder of the salt (the goal is to encase the meat in salt).
2: Roll the cloth and salt around the tenderloin, starting in the far corner. The idea is to make a compact roll. Now take the points of cloth at each end of the resulting cylinder and fold them together on top of the tenderloin. The idea is to form a tight cylindrical packet. You should do this right before your charcoal is ready. Tie the package with four 16-inch lengths of butcher’s string, then trim any loose ends.
3: Charcoal grill method: Light the coals in a chimney starter and rake them out into an even layer at the bottom of the grill. You will not need a grill grate. Lay the wrapped tenderloin right on the coals, knot side up. Grill for exactly 8 minutes. Using long handled tongs, gently turn the tenderloin package over and grill for another 8 minutes. Do not be alarmed if the cloth burns—it’s meant to. In fact, the whole shebang should look about as appetizing as a fire-charred log.
4: Gas grill method: Preheat your grill as hot as it will go. You need a “2 Mississippi” fire. There is no need to oil the grill grate. Arrange the cloth-wrapped tenderloin on the grate, knot side up. Grill until the bottom is charred black, about 8 minutes. (The grill should be covered.) Turn the package over and grill until the other side is jet black, 8 minutes.
5: Transfer the charred tenderloin to a metal platter and let it rest for 2 minutes. Lift it with tongs and tap it hard with the back of a large heavy chef’s knife (you may need to tap it several times). The burnt shell should crack and come off. Brush off any excess salt.
6: Transfer the tenderloin to a clean platter or plates. Cut into 2 or 3 pieces and serve at once.
7: Make the salsa: Place the onion, peppers, chile, garlic, cilantro, lime juice, vinegar, and salt in a mixing bowl. Toss to mix, adding lime juice and salt to taste. The salsa should be highly seasoned.