Supersonically healthy Mackerel, Herbed Feta Quinoa and Creamed spinach

Last night my husband and children went fishing on Chessil Beach with friends. In a huge break from the norm, each family came back with 28 mackerel, or thereabouts!!! Our veg garden is slightly over-run by spinach so this and its herbs added to the satisfyingly homegrown/self caught lunch.
Ingredients
Quinoa salad
120g quinoa
340ml water
glug of virgin olive …