Combine the first 5 ingredients in a small pot; bring to a boil, stirring to dissolve the sugar. Add the pears; adjust the heat so the liquid gently simmers. Cover and cook until pears are just tender, about 5 minutes. Remove from heat. Cool the pears to room temperature in the port mixture; store in the fridge until needed.
When ready to serve, remove the pears from the poaching liquid and slice and fan each one; set on a plate. Combine the vinegar, 1 Tbsp. of the pear poaching liquid, mustard, honey, salt and pepper in a salad bowl. Whisk in the oil. Toss in the salad greens. Divide among 4 salad plates; set a pear fan on top. Divide and top each salad with the walnuts and cheese and serve.
Options: Use baby spinach or chopped leaf lettuce instead of mixed baby salads greens. Use another nut in the salad, such as pecans or toasted sliced almonds, instead of walnuts. Use another type of blue cheese in the salad, such as Roquefort or Danish blue. Or, if you don't care for the intense taste of blue cheese, crumble a mild, soft goat cheese on the salad instead.