Preheat oven to 200°C, 400°F, Gas Mark 6. Whisk mayonnaise and 4 tbs of the FRANK'S RedHot® Sauce in medium bowl. Add celery, red onion and blue cheese, toss to mix. Cover and refrigerate until ready to serve.
Bake popcorn chicken as directed on package. Transfer popcorn chicken to large bowl. Add remaining FRANK'S RedHot® Sauce, toss to coat.
Remove rolls from package, but do not separate. Cut entire package of rolls in half horizontally, leaving bottom half of rolls slightly thicker than top half. Place bottom half of rolls, cut-side up, in 33x23cm baking dish sprayed with non stick cooking spray. Sprinkle half of the cheese evenly over bottom half of rolls. Top evenly with chicken and remaining cheese. Place top half of rolls on shallow baking pan, cut side down. Brush tops with melted butter.
Bake both pans 8 to 10 minutes, until lightly browned and cheese is melted. (Remove top half of rolls from oven early if they are browning too quickly.)
To serve, spread celery slaw evenly over bottom half of sandwiches. Place toasted top half of rolls on top of slaw layer, cut-side down. Secure each sandwich with a toothpick.