Preheat a grill to medium high. Soak the onion rings in a bowl of cold water. Meanwhile, combine the meatloaf mix with the diced onion, parsley, breadcrumbs, egg, paprika, 1 tablespoon each ketchup and duck sauce, 1 teaspoon salt and 1/2 teaspoon pepper. Gently form into four 1-inch-thick patties; make an indentation in the center of each.
Brush the patties with the olive oil and grill until marked on the bottom, about 6 minutes. Meanwhile, mix the remaining ketchup and duck sauce in a small bowl for brushing; set aside a few tablespoons. Turn the patties, brush with the ketchup mixture and continue grilling until cooked through, about 5 more minutes. Toast the buns, if desired.
Spread the buns with the reserved ketchup mixture. Drain the onion rings. Serve the patties on the buns; top with the onion, lettuce, tomato and pickles. Serve with sweet potato chips, if desired.
Photograph by Antonis Achilleos
Courtesy of Food Network Magazine