Spread the walnuts on to a baking tray and toast them under a preheated grill for 3–5 minutes, shaking the tray frequently to ensure that they are evenly browned and do not burn. Alternatively toast the nuts for 7–10 minutes in a moderate oven at 180°C (350°F/Gas 4). Set aside to cool.
Cut the bread slices into 4 cm (1½ inch) circles using a plain round cutter.