Preheat oven to 350 degrees. Spray a 9 x 9 inch baking dish with cooking spray.
In a large pot of boiling salted water, cook pasta according to package instructions. Drain and return to pot.
In a large skillet, melt butter over medium-high heat. Add onion, garlic, and mushrooms; cook until onion and mushrooms are beginning to soften, about 5 minutes. Add kale, cover and cook until almost tender, about 5 minutes. Transfer to pot with pasta.
Stir in ricotta, lemon zest, and 3 tbsp. Parmesan cheese; season with salt and pepper. Transfer mixture to baking dish and top with remaining cheese. Bake until top is golden, about 30 minutes.
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