Cook whole zucchini in boiling salted water until barely tender (7-10 minutes). Cut in half lengthwise; scoop squash from shells and mash.
Cook sausage with onion; drain fat. Stir in zucchini. Reserving 2 tablespoons Parmesan cheese, add remaining ingredients.
Spoon into shells and place in shallow baking dish. Sprinkle with cheese and dash with paprika. Bake at 350 degrees for 25-30 minutes. Makes 4 servings.