Place tomato slices on paper towels; sprinkle with 1/8 teaspoon salt, and let stand 5 minutes.
Place tomatoes, zucchini, and next 4 ingredients in a large bowl. Sprinkle evenly with Creole seasoning and cornstarch; shake to remove excess.
Combine breadcrumbs, 1/4 teaspoon salt, and pepper in a shallow bowl. Whisk 3 egg whites in a small bowl until frothy. Dip half of vegetables in egg whites, draining excess. Dredge vegetables, in batches, in breadcrumb mixture. Repeat procedure with remaining egg whites, vegetables, and breadcrumb mixture.
Arrange vegetables on wire racks coated with cooking spray; place racks on aluminum foil-lined pans. (Do not overlap vegetables.)
Bake at 400° for 30 to 35 minutes or until golden brown. Serve immediately with Horseradish Sauce.