Preheat oven to 400 degrees F. Grease a 2-qt. baking dish; set aside. In a 6-qt. pot cook gnocchi according to package directions, adding kale for last minute. Drain; return pasta and kale to pot.
Meanwhile, in a saucepan cook garlic in butter over medium heat for 1 minute. Stir in flour to combine. Whisk in milk; cook and stir until thickened and bubbly. Stir in Fontina and lemon zest. Pour over gnocchi mixture; stir to coat. Transfer to prepared baking dish. Top with Parmesan. Bake 20 minutes until lightly browned and bubbly.