Growing a winter green crop is something that's recommended to provide organic matter to dig into the soil in spring. Alternatively, people buy pea straw.
Personally, I don't like the idea of spending money on stuff if I don't need to, and why should a green crop not also be an edible crop?
One really good winter crop that's a legume, so will fix nitrogen, and also provide plenty of biomass, is broad beans, but not everyone likes broad beans.
I personally do, but I wasn't sure about other members of the family.
A legume that pretty much everyone likes is peas, especially the varieties you can eat in their pods such as snow peas and sugar snap peas. The only problem with these varieties is that they need staking, and if you haven't got stakes, what to do?
Turns out, there's a pretty simple solution. Broad beans grow tall, well over a metre, and if you plant some peas in amongst them, the peas will happily climb up the broad beans.
End result; lots of nitrogen rich plant matter to go into the soil later, and something to harvest that should cater to most people's tastes.