Dump everything except the bread, onions, and peppers in a large zipper bag or a bowl and mix thoroughly, refrigerate at least overnight, but 24 hours or more is better.
Fire up the grill and toast the bread on the cut side with the lid open. Watch it carefully so it doesn't burn. If it does blacken a bit, scrape off the char and the bread will be fine. Set aside on a serving platter at room temp.
Grill the peppers on both sides until they are softening but not limp. Set aside in a serving bowl at room temp.
Put the onion rings into a bowl with about two ounces of the marinade and toss them together until the rings are well coated. Grill the rings with the lid open until they are slightly soft. Set aside in a serving bowl at room temp.
Put a colander or strainer in the sink and dump the meat and marinade into it. Let the meat drain for a few minutes so it will not drip marinade onto the fire when you cook the meat. Then move the meat to the fire and separate the chunks so they are not touching. Grill on one side with the lid up until brown and until there are dark grill marks. Turn the meat over with tongs and grill some more until the exterior brown a bit.
Assemble the sandwiches by putting the meat on the bread first and topping it with the pepper and onions.
Servings: 12