Toss the bread cubes in the oil and cook in a hot frying pan for 2-3 minutes or until golden and crisp. Remove from the frying pan and drain on kitchen paper.
Melt the butter in a frying pan and add the walnuts and cook for 3-5 minutes. Remove from the frying pan and allow to cool on a plate lined with kitchen paper.
Place the lettuce leaves on a serving plate. Add the croutons, walnuts and Parmesan and drizzle over the dressing. Serve straight away.