Tuna salad sandwiches are one of my husband's favorite. This is what I use:
1 can tuna
about a quarter of a small onion, diced
1 stalk of celery, diced fine
1 TBSP of relish
1/2 TBSP of mustard
1 1/2 tsp of Oregano
Salt and pepper to taste
Mayonnaise (you can use Light Mayo)
I mix all of the ingredients together and then add the mayo until the mixture is of the desired consistancy. Hope this helps!