I think, starting in December in Zone 7, and wanting salad greens, your best bet is to plant microgreens inside. There's a thread on it here:
https://permies.com/t/94155/growing-microgreens
Otherwise, you can look at Winter Sowing, using that space (assuming puppy won't knock containers over) to get a jump on the weather -
http://www.wintersown.org/ is the classic resource but if you google "winter sowing" you'll find lots of other, sleeker, web sites.
Or once things start warming up, you could put some old windows over the bed to act as a cold frame, again to get a jump on the weather.
I'd say otherwise you're not going to be able to plant until March - radishes, frisee, and peas will start early and give you salad vegetables (pea shoots are tasty!)