In a small bowl whisk together the oil, vinegar and mustard. Season with salt and pepper to taste.
Toss the spinach with the dressing until evenly coated then divide the spinach among 4 serving plates.
Core the apple and slice it into matchsticks. Sprinkle a quarter of the apple pieces on top of each salad. Follow with the walnut pieces. Serve immediately.
Recipe courtesy of Ellie Krieger, 2007, All Rights Reserved