I love tuna casserole! Make it by marinading the tuna in lemon and salt(usually garlic too). Cook up some barley or (less healthy) egg noodles. Make a quick roux with celery. Saute minced celery in butter, add flour then milk and stir to thicken. The celery should give it good flavor. Layer the barley, tuna and thawed frozen veggies into a casserole, pour the roux on and top with some cheese. It's my guilty pleasure.
Also, maple minted carrots are delicious without onions.
Marinated canned tuna or fresh? I have spent nearly all 30 years of my life weary from my search for a good tuna noodle casserole. I have tried dozens. I need to try this but with more information