About Canteen Recovery

Yes the AAR , Kerala order no. CT531/18-C3 in case of Caltech polymer Pvt Ltd. , it's Taxable supply , but Ruling does dealt with valuation of Such supply by Employer to Employee.
As the Employer & Employee are deemed to be related person as per the explanation in Section 15 , so the valuation is to be done as per Rule 28 , the transaction value cannot be subsidised rate being charged from Employee.

So in my view GST shall be charged on atleast at the rate on which employer receiving from caterer.

* Ruling does NOT Dealt with valuation how the valuation is done.