Use a mortar and pestle to crush the oregano and cumin. Add the garlic, peppercorns and salt to the mortar and crush until you have a smooth paste. Generously smear the chops with this paste. Place the chops in a glass baking dish.
Whisk the orange juice, vinegar, and olive oil together in a small mixing bowl. Cover the pork chops with the sliced onions and the orange juice mixture. Seal the baking pan with plastic wrap and refrigerate for a minimum of 4 hours.
Remove the pork chops from the marinade. Pat them dry with paper towels. Place the marinade and the onions in a 2-quart saucepan with the tomato sauce and wine. Bring to a boil, then reduce heat to low, and let simmer, uncovered, stirring occasionally until the pork chops are cooked. Meanwhile, lightly dust the pork chops on both sides with flour. Heat some olive oil in a large sauté pan until it just begins to smoke. Quickly add the pork chops and brown on both sides. Reduce heat to medium low and continue to fry the chops until they are cooked through, about 15 more minutes.
Serve the chops with plenty of sauce poured over the top. Garnish with slices of fresh avocado seasoned with salt, pepper, and lime juice.