I did an early crop of mange tout in my tunnel, sown in February, and had a really fab crop from just one row of plants. They loved it in there. Next year I'm going to do some French beans too.
I'm also doing a few plants each of a variety of plants that are supposed to be cold loving, including Swiss chard, carrots, cabbage, kohl rabi, swede, celery, celeriac, just to see which work in there, and they're all doing very well. Most of them were in there when the temp was in the 40s in my tunnel, and it didn't seem to bother them at all.