How to Make It
Cook the spaghetti according to the package directions. Reserve ½ cup of the cooking water; drain the pasta and return it to the pot.
Meanwhile, in a large skillet, cook the leeks in the butter over medium heat until tender, 4 to 6 minutes. Add the ham, beans, and reserved cooking water, season with ¾ teaspoon salt and ¼ teaspoon pepper, and cook until the beans are just tender.
Toss the pasta with the leek mixture and the lemon zest.