As now is time of Sagardoa and a lot of people will now be in Astigarraga, Hernani or somewhere else but sure that having fun in all the Sagardotegis.
Take water in a sauce pan. Add a little salt to it and bring to boil, cook fish for a few minutes in this water till tender. Remove the bones and cut into small pieces. Take out the fish on a paper towel. Take a saucepan and heat butter in it. To this add four tbsp flour and cook for about one minute stirring continuously. Now slowly add milk to this, bring to boil and simmer for two minutes, the sauce is ready. Clean the green peppers and dice them. Melt a little butter in a pan and cook for about five to six minutes. Now add the sauce and fish in this. Season with salt. Serve hot.