Fresh green beans will provide the most crisp-tender feel, but frozen green beans can also work. I recommend transferring them in the refrigerator or placing them in a colander and running cool water over them to thaw them before using in the recipe. Either way you do it, be sure to blot them very well to remove as much excess moisture as you can. Though even with blotting, be aware previously-frozen beans will be a bit soggier than fresh.