Pipinola, chayote, mirliton. Probably other names. Can be sauteed, braised, used in soups, or stuffed and baked. Mild flavor, firm/crunchy flesh that softens with cooking. We like to cook them after they are peeled. There's also a large squash seed in the middle that you'll probably want to remove. Very easy to grow with a long enough season and very productive plant. There are a few threads featuring this veg on Gardenweb.