Wash the greens.  Slice the watercress into shorter lengths discarding the last part of the stem.  Core and slice the pear - don't peel.  Deseed the pomegranate by immersing the half of the fruit in a bowl of water and removing the seeds under water.  Pour off the water before adding to salad.  if you like roast the walnuts for 5 minutes. Mix the oil and vinegar in a jar. Assemble all ingredients on a platter and drizzle over the dressing.