Walnut Dressing: Combine walnut oil, lemon juice, mustard, sugar, salt, and pepper in a covered jar. Shake well and refrigerate.
Toss lettuce, walnuts, blue cheese, and pear in a salad bowl. Add dressing, toss, and serve immediately.
NOTE: Walnut dressing may be made up to 4 days in advance and kept covered in the refrigerator. Walnut oil should be stored in the refrigerator as it turns rancid quickly.