1. Grill the lamb steak under a moderate grill for 10 - 12 minutes, turning once.
2. Prepare the topping. Wash the spinach well, shake off the excess water and chop the leaves. Transfer to a heavy-based saucepan, cover and bring to the boil. The leaves should hold sufficient water to cook the spinach but, if necessary, add 2 teaspoons of water. Boil for 3 - 4 minutes until tender. Drain well, pressing out any liquid.
3. mix together the chopped spinach, single cream, chives, salt, pepper and nutmeg.
4. Spread the hot spinach mixture over the lamb steak, sprinkle with the grated Parmesan cheese and return to the grill for a further 1 - 2 minutes.