I think your problem is with the reference letter.
It is actually clear that the description in your reference letter may not on par with job description under NOC 6321.
Have you read the NOC qualification requirements?
Employment requirements
-Completion of secondary school is usually required.
-Cook's trade certification, which is available in all provinces and territories, or equivalent credentials, training and experience, are required.
first line says culinary school is optional, but second line clearly says you do need a certification to qualify being a chef.
Not trying to be an ass here, I think CIC has a strong case against you.
my suggestion is if money is not an issue, then go back to school get some certification or actually go through culinary school and then re-apply afterwards instead of fighting a battle that you could possibly lose.