1Heat oven to 350º. Spray 2-quart casserole or 8 x 8-inch baking dish with cooking spray.
2In 3-quart saucepan, heat oil in over medium heat. Add onions and garlic; cook 2 to 3 minutes, stirring occasionally, until onions are crisp-tender. Stir in Peperonata Sauce remaining ingredients. Simmer uncovered about 8 minutes or until slightly thickened.
3Cut polenta into twelve 1/2-inch slices. Arrange 6 slices polenta on bottom of casserole. Spread half of the sauce over polenta. Sprinkle with 1/2 cup of the cheese. Repeat with remaining polenta, sauce and cheese.
4Bake uncovered 35 to 40 minutes or until heated through and cheese is light brown. Let stand 10 minutes before serving.