Place cornmeal and 1/4 teaspoon salt in a large saucepan. Gradually add water, stirring constantly with a whisk. Bring to a boil. Reduce heat to medium; cook 10 minutes, stirring frequently. Stir in corn kernels. Set aside; keep warm.
Place each chicken breast half between 2 sheets of heavy-duty plastic wrap; flatten to 1/4-inch thickness using a meat mallet or rolling pin. Sprinkle with 1/4 teaspoon salt, chopped rosemary, and pepper.
Heat 2 teaspoons oil in a large nonstick skillet over medium-high heat. Add chicken, and sauté 3 minutes on each side or until done.
Arrange a chicken breast half and 1/2 cup polenta on each of 4 plates; drizzle 1/2 teaspoon oil over each serving of polenta. Garnish with rosemary sprigs, if desired.