Dredge the chicken in bread crumbs. In a large skillet heat the butter. When the foaming subsides, brown the chicken on all sides for about 10 minutes or until cooked through. Season to taste with salt and pepper. While the chicken is cooking, slice the bread in half vertically and then in half again horizontally and pull out all of the soft bread crumbs to create four boat like shells. Spread each "bread boat" with tartar sauce, top with chicken nuggets, then with shredded lettuce and tomato slices. Slice each piece in half again.
In a food processor or blender mince the scallion, pickle and parsley, then puree with mayonnaise and mustard and season with salt and cayenne pepper.