Bring a large pot of lightly salted water to a boil. Add penne pasta, cook for 10 to 12 minutes, until al dente, and drain. Lightly grease a medium casserole dish.
Preheat oven to 350 degrees F (175 degrees C). In a blender or food processor, thoroughly mix the Parmesan cheese and crackers.
Heat the oil in a skillet over medium heat. Place the onion in the skillet, and cook and stir until tender. Mix in the zucchini, tomato, and garlic, and season with oregano, basil, celery, salt, and pepper. Continue to cook and stir until the zucchini is tender.
In the prepared casserole dish, mix the pasta with the vegetable mixture and mozzarella cheese. Top evenly with the Parmesan cheese mixture.
Bake 25 minutes in the preheated oven, or until the topping is lightly browned. Allow to sit 5 minutes before serving.