I want to stop eating mayo for sure,
Why?
Nothing wrong with fitting full fat mayo into your daily requirement.
Tuna - water drained
Light mayo - just enough so that the tuna isn't dried out
place on 100% whole wheat bread
place lettuce on top of the tuna, cover with other slice of bread
YUM!
I also LOVE tuna melts although, I have never tried it on a bagel...