In a medium saucepan, combine corn, onion, green pepper, and water. Bring to a boil; reduce heat to medium-low. Cover and simmer 5 minutes or until vegetables are crisp-tender. Do not drain.
In a a large mixing bowl, combine squash, tomato, 3/4 cup cheese, cornmeal, milk, eggs, salt, pepper, and hot pepper sauce. Add corn mixture to cornmeal mixture; stir to blend.
Pour into a greased 1 1/2-quart casserole dish. Bake, uncovered, at 350° for 45 to 50 minutes or until heated through. Top with remaining cheese, and, if desired, tomato slices and green pepper rings.