In a large bowl, combine lettuce, apple, grapes, cheese, celery, and walnuts.
In a small bowl, whisk together oil, vinegar, mayonnaise, sugar, and salt until smooth and creamy.
Drizzle salad with dressing, and toss to coat. Any remaining dressing can be stored in the refrigerator for 2 to 3 days. Garnish with pepper just before serving.