Preheat oven to 350 degrees Fahrenheit. Grease an 8- x 8-inch pan.
Heat a 10-inch greased skillet over medium heat. Sauté celery and onion in oil until tender, stirring occasionally.
In a large bowl, finely flake tuna with fork. Add celery and all remaining ingredients. Mix until well blended.
In a small bowl, with mixer at high speed, beat egg whites until stiff peaks form.
Fold egg whites into tuna mixture. Pour tuna mixture into pan.
Bake for 50 minutes to one hour or until done.
Styling and Photography by Sarah Braun