Cover potatoes with water; bring to a boil. Cook potatoes until a knife can penetrate to center of potato (potatoes will cook further on the grill). Cool.
Cut potatoes into 1/2-inch thick slices. Toss gently with 1/4 cup Marie’s Chunky Blue Cheese dressing. Grill potato slices. Cool thoroughly; cut into chunks.
Combine remaining 1 cup Marie’s Chunky Blue Cheese dressing, mustard, celery, green onion, bacon and black pepper in a bowl. Pour over potatoes and toss gently to combine. Sprinkle with parsley and chill.