Toast the slide of bread until just golden. Set aside.
Preheat toaster oven or broiler.
Combine tuna, onion, celery, red pepper, dried cranberries, hot sauce, and mayo in a bowl. Season with salt and pepper to taste.
Spoon tuna mixture onto toasted bread. Top with tomato and cover in cheese. Place in preheated toaster over/broiler until cheese is melted and just turning golden brown.