Its Chinese name is "莴笋 wosun."
Remove the leaves from the stem (you can use these in salads, or cook/wilt them down and use in stir fries or soups as well).
For this dish, you can prepare any type of stir fry you like - any protein, sauce, other veggies, etc.
For my favorite stir fry recipe, check out this blog post, and substitute the celtuce stems for broccoli (or add them in addition to broccoli).
To prepare and stir-fry celtuce stem:
Mix things up by using different stir fry sauces.
If you don't like the soy-sauce based sauce in the beef & broccoli recipe, you can use a bottled teriyaki sauce, add the celtuce stem to orange chicken, or make a honey sriracha sauce!