This is a fantastic recipe that is so quick and so simple and uses our reliable friends the frozen peas, which work really well here. Great with fish, meat or even as a vegetarian dish with a big dollop of butter on top.
Heat the oil in a pan and add the chopped onions, mint, and peas. Cover and leave for a few minutes to steam. Mash with a potato masher. You can do this with a food processor as well, just pulse it until smooth. Whether mashing or pulsing, when it's done add the butter and season very carefully, to taste.