I LOVE cilantro.
AND it's actually really good for you:
15% of folates,
11% of vitamin B-6 (pyridoxine),
45% of vitamin C,
225% of vitamin A,
258% of vitamin K,
22% of iron and
18% of manganese.
The leaves and stem tips are also rich in numerous anti-oxidant polyphenolic flavonoids such as quercetin, kaempferol, rhamnetin and epigenin.
Cilantro herb contains no cholesterol; but is rich in anti-oxidants and dietary fiber which help reduce LDL or "bad cholesterol" while increasing HDL or "good cholesterol" levels." -http://www.nutrition-and-you.com/cilantro.html
ACTUALLY, when you look up cilantro on google, some of the first links that pop up recommend using it as a form of oral chelation (removal of toxic metals we encounter in our environment).
Cilantro is most typically used in mexican food here, so if I were going to use it in a chicken salad sandwich, I would add it with onion and red pepper- not sure how much spicyness you can take, but I'm in LOVE with chipotle peppers lately, they have very distinctive, sweet flavor in addition to the spicyness and you only need a little bit. I get them in a can smaller than a tuna fish can in the ethnic food aisle at Meijer.
Another route would be to add a little lime juice - but not too much or it will actually cook the chicken more and make it tough.
I would top that mix with lettuce and tomato and maybe spread some avocado on the sandwich buns. :)