Preheat the oven to 450 degrees F. Line a large baking sheet with parchment paper.
Combine the buttermilk, hot sauce and egg white in a pie dish. Mix the cornmeal and salt in another pie dish. Dip the tomato and zucchini slices into the buttermilk mixture, and then into the cornmeal, gently turning to coat.
Spray a large nonstick skillet with nonstick cooking spray over medium-high heat. Add half the tomato and zucchini slices in a single layer and cook until browned on both sides, 3 to 4 minutes.
Transfer the slices to the baking sheet and bake until the tomatoes and zucchini are golden brown on both sides, about 8 minutes. Wipe the skillet clean and repeat with remaining vegetable slices. Serve hot.