The night before you plan to cook the meat, place it in a shallow, nonreactive dish. Combine the marinade ingredients in a bowl and pour the marinade over the meat. Refrigerate, covered, for at least 12 hours and preferably 24.

Prepare the salsa by combining all the ingredients in a bowl. Refrigerate until ready to serve.

Drain the meat and discard the marinade.

In a large, heavy skillet or wok, warm the oil over high heat until it just begins to smoke. Sauté the beef in two batches, tossing almost constantly, until browned well, about 2 minutes per batch. Transfer the beef pieces to a plate as they brown.

Reduce the heat to medium and add the onion and chiles to the skillet. Cook until softened, stirring almost constantly. Return the beef to the skillet and toss with the vegetables.

Using tongs, lift about one-quarter of the beef mixture from the skillet, allowing any excess juices to drip back into the skillet, and fill a tortilla. Repeat with the remaining beef mixture and tortillas. For stand-up eating, Roque bunches aluminum foil around the tortillas.

Serve immediately, topped with salsa.

Regional Variations: Roque Garcia’s carnitas bear a resemblance to a venerable northern Mexico dish called cortadillo, which is also sold in street stands, partially as a hangover cure. The beef usually isn’t marinated, and it’s likely to be cooked in lard, but the rest of the preparation and ingredients are similar except for the addition of tomatoes.