Arrange 1 cup gourmet salad greens on each of 4 plates. Finely chop 2 ripe Bosc pears; toss with 2 teaspoons lemon juice. Divide pears, 6 finely chopped pitted dates, and 2 tablespoons chopped walnuts evenly among salads. Combine 1 1/2 tablespoons extra-virgin olive oil, 2 teaspoons sherry vinegar, 1/4 teaspoon salt, and 1/8 teaspoon black pepper; stir with a whisk. Drizzle evenly over salads. Top each salad with 1/2 ounce shaved Manchego cheese.