Baked Polenta with Eggplant and Red Bell Peppers

1. Place the eggplant cubes in a colander, sprinkle with salt, toss, and let rest for at least 30 minutes to drain excess moisture.
2. Preheat oven to 450°F (230°C, Gas Mark 8). Spray the peppers with cooking spray and place in an ovenproof skillet or roasting pan. Roast about 8 minutes to blister and blacken the skins. Using tongs, turn the peppers over and roast 7 minutes more. Do not over roast. When cool enough to handle, pull out the top stem and remove the seeds and skin. Pat dry. Cut into 1-inch dice and set aside.
3. Spray a large skillet with cooking spray and place over medium-high heat. Add the drained eggplant and cook for 2 minutes, stirring. Add the garlic and thyme. Cook 2 minutes more, until the eggplant is soft. Remove from the heat and add the roasted peppers.
4. Fill a 3-quart (3 l) pot with chicken broth. Bring to a boil. Add the polenta in a steady stream, whisking until smooth. Cook over medium low heat for 15 minutes, stirring frequently with a wooden spoon or spatula. Pour into a large baking dish or casserole. Spread the eggplant-pepper mixture evenly over the polenta, pressing it down with a wooden spoon. Top with the mozzarella cubes, pressing lightly. (Dish can be assembled to this point, covered, and refrigerated 1 day ahead. Increase the baking time by about 20 to 25 minutes if the unbaked casserole is cold.)
5. When ready to bake, preheat the oven to 375°F (190°C, Gas Mark 5). Bake the casserole for about 25 minutes, until the cheese is melted.