Plenty of nice places in Bilbao. Loved this place https://jatekobilbao.com/. Unassuming bar with a little restaurant at the rear. No one spoke English, but one of the best value lunches I have had anywhere.
Also waiting on this one - LGW to Biarritz late May, with Bilbao as a backup. Have accommodation for a week in San Sebastian, but need flights for 5 and Easyjet, is my best bet. Apparently they usually release Summer in the September, but no sign of it yet.