Heat oven to 400°F. Spray 1 1/2-quart gratin or baking dish with nonstick cooking spray. Place zucchini in large strainer set over bowl; let stand 10 minutes. Press or squeeze zucchini to remove excess liquid.
In large bowl, whisk eggs until blended. Add sour cream, cheese, onion, butter and salt; stir until combined. Stir in zucchini and cornmeal until blended. Pour into gratin dish.
Bake 25 minutes or until edges are golden brown and knife inserted in center comes out clean.