In a nonstick skillet coated with cooking spray, saute onion and garlic until tender; remove from the heat. Stir in parsley and orange zest.
Place halibut in an 11x7-in. baking dish coated with cooking spray. Top with onion mixture. Combine orange and lemon juices; pour over fish. Sprinkle with salt and lemon-pepper. Cover and bake at 400° for 15-20 minutes or until fish flakes easily with a fork.