Wash hands with soap and water.

Preheat oven to 350 °F.

Drain tuna and break the meat apart with a fork.

Wash and chop the celery and shred the cheese.

Mix tuna, celery, cheese, light mayonnaise, dried onion, salt, and pepper into a medium mixing bowl with a wooden spoon.

Wrap each sandwich on a square of aluminum foil, folding edges securely.

Bake about 20 minutes or until hot in the middle. Cool slightly before serving.