Preheat oven to 350 degrees. Butter a 2-quart baking dish. Stir lime zest and juice and diced pineapple into batter. Spread in baking dish. Bake 15 minutes, then remove from oven and quickly arrange pineapple rings on top. Bake until top is golden brown and a toothpick inserted in center of cake comes out with a few moist crumbs attached, about 25 minutes. (Tent with foil if browning too quickly.) Let cool in dish on a wire rack 20 minutes. Dust with confectioners' sugar, if desired.