Preheat Oven To Broil. In A Bowl, Mix Together Tuna, Celery, Mayonnaise And Salt. Spread Tuna Mixture Onto The Toasted Muffin Halves And Place Them On A Baking Sheet. Top Each Half With A Slice Of Tomato And A Slice Of Cheese. Broil Until Cheese Is Melted, About 3 To 5 Minutes.