In a blender, combine the achiote, chiles, canning sauce, oil and ¾ cup water. Blend into a smooth marinade. With a heavy mallet pound the meat to about 1/8-inch thick. Use 1/3 of the marinade to smear over both sides of each piece of meat and sprinkle with salt. Cover and refrigerate at least an hour for the flavor to penetrate the meat. (In a container with a tight-fitting lid, refrigerate the rest of the marinade for another use.)
Heat a gas grill to medium-high to high or light a charcoal fire and let it burn until the coals are covered with gray ash and are very hot. Brush or spray both sides of the onion and pineapple with oil. Grill, turning regularly for several minutes, until they are richly colored and softening—you want them to still have nice texture. Cut the core out of the pineapple, then chop the onions and the tender pineapple into small pieces. Keep warm on the side of the grill.