In a medium-sized mixing bowl, combine the mayonnaise or yogurt with the lemon juice, kosher salt, and freshly ground black pepper. Whisk until the dressing is smooth and evenly blended.
Add the chopped apples, celery slices, halved grapes (or raisins), and toasted walnuts to the bowl. Stir gently to coat the ingredients thoroughly with the creamy dressing, ensuring an even distribution of flavors.
Prepare a bed of crisp lettuce leaves on a serving platter or individual plates. Spoon the dressed salad over the lettuce, arranging it neatly for an attractive presentation. Serve immediately for the freshest taste and texture.