Cook pasta according to package instructions; drain thoroughly.
In a skillet, cook sausage and onion until no longer pink, stirring to break up sausage as it cooks. Add zucchini; cook and stir for 1 minute. Drain meat and remove from skillet.
In same skillet arrange half of the lasagna noodles on the bottom of the skillet. Cover with half of the pasta sauce. Ladle cooked meat over sauce. Spoon ricotta atop meat mixture and then sprinkle with 1/4 cup mozzarella cheese.
Arrange remaining lasagna noodles on top. Top with remaining pasta sauce and mozzarella cheese. Sprinkle with Parmesan cheese.
Cover; cook over medium heat about 10 minutes, or until cheese is heated through. Remove from heat, let stand uncovered for 10 minutes before serving.