Preheat your overhead grill (broiler) on the highest heat.

In a medium bowl mash drained tuna with a fork. Stir in mayo and grated cheese.

Place bread on an oven-proof baking tray or sheet (lined with foil for easier cleanup). Press tuna mixture on top of the bread.

Place your prepared bread under the grill and leave until the topping is all melted and browned in places.

Scatter with salad leaves and serve with lashings of black pepper.