4 slices multi-grain bread
1 can tuna
3 tbsp greek yogurt
1 tbsp mayonnaise (add more if you want)
1 tsp mustard
salt and pepper
[also try relish as the sauce on tuna, it is sweet some like it some don't, I don't]
Mix everything but the bread and lettuce in a bowl and put it half and half on two pieces of bread, top with lettuce, and put finish the sandwich.