Preheat oven to 400°. Coat a 2-quart shallow baking dish with cooking spray, and alternately layer sliced zucchini, corn kernels, and sliced tomatoes. Combine panko and Parmesan, and sprinkle on top. Bake, uncovered, in the center of oven 30 minutes or until top is golden brown. Cover with foil, and bake for 10 minutes more or until vegetables are tender. Serve immediately.