Roast the onions. Light a charcoal fire and let it burn until all the coals are medium-hot and covered with gray ash. Nestle the onions directly in the coals and let them roast, turning as needed, until charred on the outside and soft within, about 20 minutes. Remove and cool until handleable.
Prepare and cure the meat. While the onions are roasting, lay a piece of plastic over each slice of meat while you pound it with a mallet or side of cleaver (or even the bottom of a small saucepan) to about 1/8-inch thick. Lay them in a single layer on your cutting board, then sprinkle evenly with 1 scant teaspoon of salt, flip the pieces over and sprinkle with a second scant teaspoon of salt. Collect them into a non-aluminum baking dish—a 13x9-inch pan is perfect. Cover, set aside at room temperature and set a timer for 45 minutes, the right amount of time for the meat to cure.
Marinate the onions. When the onions have cooled some, cut off the tops and bottoms, make a slit in the side and peel away and discard the charred outer layers. Chop the soft onion into roughly ½-inch pieces, scoop into a bowl season with 3 or 4 tablespoons of the juice. Taste and season with salt, usually a scant ½ teaspoon.
Make the meat marinade. In a small bowl, combine ⅓ cup of the sour orange, the pepper and the garlic.
Prepare the vegetables. In a large bowl, toss the cabbage with the cilantro and the remaining juice. Taste and season with salt, usually a generous ½ teaspoon. Spread onto a large serving platter about 14-inches or so in diameter. Decorate the perimeter with alternating slices of tomato and avocado, and sprinkle them with salt and pepper.
Grill and serve the meat. When the 45 minutes have passed, stoke your fire with a little new charcoal if necessary so that it is really hot. Pour the juice-pepper-garlic mixture over the meat, lifting the meat up to ensure that both sides of each piece are coated with juice. Let marinate 10 minutes—no more. Working with a few pieces at a time, grill the pork: remove it from the marinade, letting most of the liquid drip off, then lay onto the hot grill grates. Let sear and char a little on one side (1 to 2 minutes, depending on how hot the fire is), then flip the pieces over and sear on the other side. (The total cooking time for 1/8-inch pork pieces over a very hot fire will be no more than 2 or 3 minutes.) Lay the meat slightly overlapping down the center of the platter and pile the onions over the meat. Decorate with a few cilantro sprigs and serve without delay, accompanied by roasted habanero salsa, chiltomate and baskets of hot tortillas.