Place walnuts onto a baking tray and toast under the grill, turning occasionally. Once walnuts are evenly toasted set aside to cool.
Wash watercress, discard the bottoms of the stokes and place in a colander to drain. Wash and slice the persimmons, cut each half into four to six slices. Place watercress into a salad bowl, top with persimmons, crumbled gorgonzola and toasted walnuts. Drizzle with oil and vinegar, then season with salt and pepper.