Ronald said:
I usually need about 2 tablespoons of mayo for my 1 can of tuna, am I using too much? Should i be using something else, and if so, what?
Depends...
If it is whole fat mayo then 1 tbs is about 12g of fat - which means you are getting 24g of fat from the mayo alone...
If the mayo is a good one (made with olive oil, whole eggs and that is about it) then the fats will be healthy, but whether or not you need that much fat will depend on your total daily diet, your calorie intake and your body's requirements. I would think that you probably do not need that much fat in one meal... So cutting it back to 1 tbs may be a good idea.
If the mayo is a bad mayo (made with less than ideal oils, and with things such as sugar added to it) then you are best to take it out altogether.
Other things you can add? You mean besides some vegetables?

...
Well, for flavour, there are spices and herbs such as black pepper, chili, dill, basil, chives, mint etc... or you could add a low calorie condiments such as some mustard, wasabi paste, lemon juice, balsamic vinegar, lime juice, low-salt soy sauce... etc etc... You could also try adding a little salsa or salt-free tomato ketchup or something... Other fats you could try would be some avocado (2 tbs mashed is about 9g fat) or 1 tbs some olive oil (make a dressing with some vinegar).