1. Preheat oven to 375°.
2. Cut zucchini in half lengthwise; cut diagonally crosswise into 1/4-inch slices. Cut polenta crosswise into 8 slices; coat both sides of each slice with cooking spray.
3. Heat a large nonstick skillet over medium-high heat. Add polenta slices; cook 3 minutes on each side or until lightly browned. Arrange polenta slices in an 11 x 7inch baking dish coated with cooking spray.
4. Reheat pan over medium-high heat. Add beef to pan. Cook 4 to 5 minutes, stirring to crumble; remove from pan, and drain, if necessary. Add zucchini to pan; sauté 3 to 4 minutes or until tender. Add beef, pasta sauce, and pepper; cook 1 to 2 minutes or until thoroughly heated, stirring occasionally. Spoon beef mixture over polenta; sprinkle with cheese.
5. Bake at 375° for 18 to 20 minutes or until bubbly and cheese melts.
As a shortcut to making polenta from scratch in a saucepan, use precooked polenta. Look for flavored or plain 17-ounce tubes in the produce section of your supermarket. This precooked polenta works well in recipes that call for it to be cut into slices or cubes and sautéed, baked, or grilled.