Heat gas or charcoal grill. Cut polenta into 8 (1/4-inch-thick) slices. Brush polenta slices, corn, zucchini, bell pepper and onion with 3 tablespoons of the dressing.
Carefully brush oil on grill rack. Place polenta and vegetables on grill over medium heat. Cover grill; cook 15 to 20 minutes, turning occasionally, until polenta is browned and vegetables begin to char.
Cut kernels from ears of corn; coarsely chop zucchini, bell pepper and onion. In large bowl, toss vegetables, tomatoes, basil and remaining 1 tablespoon dressing.
On each of 4 plates, place 2 polenta slices; top each with 1 1/4 cups vegetable mixture and 2 tablespoons cheese.