Preheat oven to 400 degrees. In a 5-quart pot, cook sausage over medium heat, stirring often, until browned, about 5 minutes. Stir in onions; cover, and cook until softened, 5 minutes. Uncover; cook, stirring occasionally, until golden brown, 10 to 15 minutes. Add garlic; cook 2 minutes. Transfer to a large bowl.
Add kale and 1/2 cup water to pot; season with salt and pepper. Cover; cook over medium-low heat, tossing occasionally, until tender, 10 to 15 minutes. Drain; coarsely chop. Transfer to bowl with onions.
Meanwhile, cook noodles 2 minutes less than package instructions. Drain; rinse under cold water.
Add noodles, tomatoes, and ricotta to the bowl; season with 1 1/2 teaspoons salt and 1/2 teaspoon pepper. Toss well. Pour into a 9-by-13-inch baking dish; smooth top with a spatula. Sprinkle with Parmesan. Bake until golden brown, about 40 minutes. Cool 10 minutes before serving.