Coat a 9×13-inch baking dish with nonstick cooking spray.
Layer leeks, carrots and olives in baking dish. Top with fillets. Drizzle fillets evenly with lemon juice, and season with oregano, and pepper to taste. Pour broth into bottom of dish. Cover tightly with foil.
Bake 15 minutes or until fish flakes easily with a fork.
Transfer fillets and vegetables to a platter, and serve.