I grow all kinds of lettuces almost year-round here in the south bay and it is very easy to do. We really can harvest lettuce and other salad greens such as arugula, cilantro, mache, from March – November. I find that things really slow down December – February. Peas of all kinds, including sugar snaps, sugar peas, sweet peas (ornamental), shelling peas, etc. are ideally planted from seed in August or seedlings should be planted in Sept and October to mature and fruit or flower in February or March through May or early June at which time they start getting a lot of powdery mildew and need to come out and make way for summer vegetables.
Enjoy your winter vegetable gardening!