i never tried that but I wouldn't cook any thing for chickens. I don't think is necessary if they don't eat it you will know what they like
i think very young beans will be the best.Mine love tomatoes the redder the better
Bean seeds have what are called, "anti-nutrients." They are inactivated by heat. Some beans have more anti-nutrients than others.
These components of the beans interfere with the digestion of other nutrients in the diet. But, these are found in mature seeds. I doubt if the same factors amount to much in greenbeans.
Greenbeans and most vegetables contain quite a bit fiber and the chicken's digestive system doesn't make very good use of fiber. Of course, cooking would break down some of the fiber making it more digestible. Still, it probably wouldn't be a good idea if the chicken's diet contained a whole lot of vegetables of any kind. They only have so much capacity for their food and need nutrition not just for body maintenance but to grow and produce eggs.