Preheat oven to 425F. In a 13X9X2-inch baking dish layer onion, zucchini and garlic. Drizzle with 2 tablespoons of the oil; sprinkle with 1 1/2 teaspoons of the lemon-herb seasoning. Bake 12 minutes.
Remove baking dish from oven. Add tomatoes; stir. Top with fillets and drizzle with remaining 1 tablespoon oil. Sprinkle with remaining 1/2 teaspoon lemon-herb seasoning and season with pepper to taste.
Pour broth around edges of baking dish. Return dish to oven and bake 10 minutes or until fish flakes easily with a fork. Serve hot.