I can't emphasize enough how well lettuce does in a container. I like the Earthbox brand but I'm sure that something else could be rigged that would work just as well. This planting has been snipped back practically to bare earth 3-4 times and it just keeps coming back. Just buy a packet of mixed leaf lettuce seeds from one of the big seed companies and plant according to the directions.
Here in west central Georgia it is already hot as Hades and I do believe I'm going to be able to keep a little bit of lettuce going until the first tomato is ready. Something I've never been able to do growing lettuce in the main garden. Plus, it's right there on the deck!