Restaurant staff where very knowledgable where we stayed, and I took a picture of the gf aisle in a supermarket as it was enormous. Even the small supermarkets seemed to have some gf stuff.
We were self catering and took sandwiches e.g. when we went on the Bulnes furnicular, ate ice creams at the cafe at the top.
Potes is more touristy than Cobreces so I think it will be even easier to cater gf, but would take some stuff just in case.
We self-catered and I had a great time doing paella using the local chorizo, which I now know is heresy.
(Hope you're not vegetarian/too squeamish but when you buy chicken joints over there they cut up the chicken in front of you at the meat counter.)
Have a great time!