Preheat oven to 350 degrees.
Slice tops off of the tomatoes and scoop the pulp out of the centers to make stuffable shells; set aside. Discard half of the tomato pulp then remove seeds from remaining pulp and chop finely; set aside.
In a medium bowl, whisk together egg and Ricotta until smooth; stir in red onion, basil, half of the Parmesan and the garlic.
Add corn, diced zucchini, and chopped tomato pulp; blend well.
Fill each tomato shell just to the top with about 1/2 cup of the Ricotta mixture then sprinkle with remaining Parmesan cheese; top each with 3 zucchini slices and a tomato top.
Place in a large baking dish; bake for 45 minutes or until filling is puffed up and tops are browned. Let stand for 10 minutes before serving.
Garnish each tomato with 1 teaspoon of chopped chives and 1 teaspoon of chopped oregano.