Green tomatoes
There's a couple of things you can do with green tomatoes that don't add much in the way of carbs.
Sauteed
Chop them and saute them in light oil with chopped onion, garlic, squash, eggplant, okra, whatever else you might have on hand.
Cobbler
Yes, cobbler. You can pretty much use any recipe for cobbler, just use a low-carb flour such as Carbquik for the crust, and substitute green tomatoes and rhubarb for the fruits. Add some cinnamon, maybe a little clove, and some extra substitute brown sugar sweetener.