Cook pasta and squash according to package directions. Meanwhile, in a large skillet, heat oil over medium heat. Add sausage and onion; cook and stir until sausage is browned and onion is tender; keep warm., In a small bowl, mix the cooked squash, cheese, salt, parsley and pepper until blended. Drain pasta; transfer to a serving plate. Spoon squash mixture over pasta; top with sausage mixture. If desired, sprinkle with additional cheese and parsley.