You could sow any of the following :- Lettuce, leaf Beet, chard, endive, chicory, Florence fennel, chervil, coriander, land cress, wild or salad rocket, Chinese cabbage and spinach. You might get a crop of carrots in but they won't be massive - and they will taste good! You can start most of the above in modules and then plant them out to avoid the worst of the pests. Slugs will walk a mile over broken glass for Chinese cabbage!