1 (6 1/2 oz.) can tuna, drained
3/4 c. ketchup
3/4 c. American cheese (4 slices)
1/2 c. chopped celery
2 tbsp. finely chopped onion
5 hamburger buns

In bowl, combine ingredients in order given. Split hamburger buns, fill buns with tuna mixture. Wrap each in foil. Bake in preheated 375 degree oven for 20 minutes or grill 15 minutes over medium coals, turning once.