Preheat oven to 350. In a large pot of boiling salted water, cook pasta to package directions and drain. Return to pot. In a large skillet melt butter over medium-high heat and add the onion and garlic. Cook until onion is beginning to soften, 4 minutes or so. Add kale, cover and cook until almost tender, about 5 minutes. Transfer to pot with pasta.
Stir in chicken, ricotta, lemon zest, and 1/2 cup parmesan cheese and season with salt and pepper. Transfer mixture to a 9x13 baking dish. Top with remaining cheese and bake until top is golden, about 30 minutes.