For the bread pudding: Whisk together the half-and-half, limoncello, granulated sugar, vanilla, lemon zest, salt and eggs in a large bowl.
Butter a 2-quart casserole dish and add the bread cubes to the dish. Pour the custard over the bread and let stand 20 minutes.
Preheat the oven to 325 degrees F.
Cover the dish with foil. Bake, covered, for 20 minutes, then uncover and continue to bake until puffed, set and golden on top, about 25 minutes more.
For the glaze: Whisk together the confectioners' sugar, limoncello and lemon zest in a small bowl. Pour the glaze on the warm bread pudding and serve.