Preheat oven to broil. Place tuna in medium bowl and flake with fork. Add celery, red onion, hot pepper flakes and mayonnaise; mix well.
Place bread on baking sheet. Spread tuna mixture on bread slices; sprinkle with cheese. Broil until cheese is melted and turning golden.
Replace canned tuna with 1 can (796 mL) chickpeas pulsed in a food processor until finely chopped.