Preheat the oven to 375°F. Lightly oil a shallow 10-inch square baking dish or round pie pan.
Bring the water to a boil in a large saucepan over high heat. Lower the heat to medium, add the salt, and slowly whisk in the cornmeal, stirring constantly. Decrease the heat to low and continue to cook, stirring frequently, until thick, about 20 minutes.
Stir in the scallions, basil, and oregano, and season with salt and pepper to taste. Spoon the polenta into the prepared pan and spread it evenly.
Arrange the artichoke and tomato slices on top of the polenta.
Season with salt and pepper to taste and sprinkle evenly with the olives and bell pepper.
Sprinkle with the cheese, if using.
Cover and bake for 15 minutes, then uncover and continue baking for 10 minutes longer to lightly brown the top. Serve hot.