Preheat oven to 375°. Spray baking pan with no-stick cooking spray. Place haddock on prepared pan. Season, if desired, with salt and black pepper. Combine 2 teaspoons orange zest and margarine. Spread over haddock. Bake 25 minutes or until fish flakes with fork.
Meanwhile, prepare Knorr® Hollandaise sauce mix according to package directions, adding orange juice and remaining zest. Serve with haddock.