Place whole zucchini in a medium saucepan with boiling salted water. Cook 10 minutes or until tender. Drain.
Cut zucchini in half lengthwise. Scoop out pulp, leaving firm shells; chop pulp.
Combine chopped pulp, cracker crumbs, onion, 1/2 cup cheese, parsley, butter, salt, pepper, and eggs; mix well.
Place zucchini shells in a lightly greased 15-x 10-x 1-inch jellyroll pan. Spoon zucchini mixture into shells; sprinkle with additional Parmesan cheese. Bake at 350° for 30 minutes or until stuffing is lightly browned. Serve immediately.