Preheat oven to 425°.
Combine first 7 ingredients in a large bowl; toss gently to coat. Arrange vegetable mixture on a foil-lined jelly roll pan. Bake at 425° for 15 minutes or until vegetables are tender and begin to brown. Drizzle with vinegar, tossing to coat.
Meanwhile, combine vegetable broth and 1 3/4 cups water in a large saucepan; bring to a boil.
Combine cornmeal and remaining water, stirring until smooth; gradually stir into vegetable broth mixture. Bring to a boil; reduce heat to medium, and cook, stirring constantly, 3 minutes or until very thick. Remove from heat; stir in half-and-half, cheese, pepper, and salt. Spoon polenta onto plates and top with roasted vegetables.