My girls really enjoyed my winter garden - broccoli, cauliflower, cabbages. The broccoli did really well this year, and only stopped producing side shoots when the weather started turning warm.
They also ate quite a bit of mustard & collard greens. Now, it's just too hot to grow any greens, so occasionally I'll buy a bunch of mustard greens tie all the stalks together & hang them also. For some reason, they seem to like their veggies hanging up!
With my summer veggies, they've been attacking the soybean plants that I grow for edamame, so I sometimes pull off a few leaves to feed them. They enjoy the cantaloupes that really didn't turn out good enough for us to eat. And any unused tomatoes - but only if they're ripe. The garden is a great place for chicken feed!