For the sauce and chicken: Heat the canola oil in a saucepan over high heat. Add the onions and cook until browned, 8 to 10 minutes. Stirring constantly, add the ketchup, pepper jelly, vinegar, honey, Worcestershire, mustard and some salt and pepper and cook until warmed through. (At this point, either use immediately, or store in the refrigerator for a few days.)
Add the meat to the warm sauce. Stirring well, cook until the sauce and meat are heated through, about 5 minutes.
For the fried onions: Heat the canola oil in a large saucepan until it registers 350 degrees F on a candy or deep-frying thermometer.
Mix some salt into the flour and spread on a plate. Dredge the onion rings in the flour and drop them one-by-one into the oil until you have a small batch. Cook until the rings are golden, 3 to 5 minutes. Remove with a slotted spoon and drain on paper towels. Repeat with the remaining onions.
To assemble the sandwiches: toast the buns, spoon the saucy meat onto the buns and top with onion rings, lettuce and tomato slices.