Cut polenta into 1/4-inch-thick slices (about 24). In medium-size bowl, combine chicken, salsa, cilantro and cumin until well mixed.
In 11 x 7 x 2-inch baking dish, arrange half of the polenta slices over bottom. Drizzle 1/3 cup of the heavy cream over polenta. Top with half of the beans and half of the corn. Spread with half of the chicken mixture. Sprinkle with half of the scallions and 1 cup of the shredded cheese. Repeat layering: polenta, cream, beans, corn, chicken mixture, scallions and cheese. Cover dish with nonstick foil. Refrigerate overnight, if desired.
Heat oven to 375 degrees F. (If casserole was refrigerated, let stand at room temperature 30 minutes.)
Bake, covered, in 375 degree F oven until internal temperature registers 130 degrees F on instant-read thermometer, about 50 to 60 minutes. Let stand 10 minutes before serving. Makes 8 servings.