Preheat oven to 325 degrees F (165 degrees C). Grease a deep 9x13 inch baking pan.
To prepare the sauce, cook and heat chopped onions in a large skillet over medium high heat for 5-10 minutes, until caramelized. Add in mushrroms; cook and stir until mushrooms soften. Stir in pasta sauce and salt to taste. Bring to a boil; reduce heat and simmer sauce for about 10 minutes, stirring frequently.
To assemble lasagna, spread 1/2 of the sauce into the bottom of prepared pan. Then layer 1/2 chopped kale, 1/2 the zucchini slices, and 1/2 the ricotta mixture..Repeat by layering the remaining sauce, kale, zucchini slices, and ricotta mixture,. Spread Parmesan cheese evenly over the top; cover with foil.
Bake for 45 minutes. Remove foil; raise oven temperature to 350 degrees F (175 degrees C), and bake an additional 15 minutes. Let stand for 5 minutes before serving.