Prepare the salad dressing just before use. Add vinegar, apple juice, Dijon mustard, salt, and pepper 1 at a time through the feed opening of a running blender. Then, leaving the blender running, add the olive oil in a slow steady stream.
Cut the potatoes into 1/4-inch thick slices and add to a mixing bowl. Slice the green beans into 3/4 to 1-inch lengths and add to the potatoes. Fold in parsley and tuna. Toss gently with enough dressing to coat and top with wedges of hard boiled egg.
Recipe courtesy of Robert Irvine with Brian O'Reilly, Harper Collins Publishers, copyright 2007.