When I had hens I would bag my lawn clippings and dump them in a pile in the run. Adding compostable kitchen scraps would attract flies and the chickens would dig through the pile to get maggots and other insects. I, of course, supplemented with laying mash, but very little. I have also seen people use meat scraps to incubate huge numbers of soldier fly larvae that are gathered using a special trap device. This is difficult in the winter I would presume. I live in the deep south so sub 40°F weather is uncommon even in the coldest days of winter. After a couple weeks of the chickens rummaging through the clippings, I would gather all the remains and let them cool prior to dressing my garden. The chickens are good at turning the compost in their hunt for critters and it would compost rather quickly. Joel Salatin has good information on this type of system.