- 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 on serving plates.
- Toast walnuts in a dry skillet over a medium-high flame until fragrant, about 2 minutes, set aside.
- Core the apple and slice it into matchsticks, and sprinkle a quarter of the apple pieces on top of each salad, follow same with the walnut pieces.
- Serve immediately.