Step 1Wash the spinach well and dry thoroughly. Tear the leaves into bite-size pieces and place in a large salad bowl.
Step 2Cut the papaya in half and scrape out the seeds, reserving 1 1/2 tablespoons. Peel the papaya and cut it lengthwise into quarters, then crosswise into slices about one-fourth-inch thick. Add to the spinach and toss.
Step 3Combine the vinegar, shallot, sugar, mustard and Worcestershire sauce in a blender. Blend the mixture thoroughly. With the blender running on low speed, add the oil and blend until emulsified. Add the papaya seeds and blend until they are coarsely chopped. Season with one-fourth teaspoon salt, or to taste.
Step 4Toss the salad with half the dressing. Add more to your taste. Sprinkle with the cashews and serve.