TUNA NICOISE SANDWICHES

2 T. Miracle Whip or mayo 2 T. Dijon mustard 1 (6-oz.) can chunk white tuna packed in water, drained 1 green onion, sliced 1 celery stalk, chopped 2 T. minced pitted kalamata olives 2 T. drained capers 4 slices…