1. In a pan at medium heat, cook the Grenoble walnuts in 1 tbsp. of olive oil for about 2-3 minutes or until golden. Set aside.
2. In a small bowl, add the remaining olive oil and the Dijon mustard. Wisp until the oil has incorporated. Add the balsamic vinegar and the maple sirup, wisp. Season with salt and pepper to your taste. Set aside.
3. In a big salad bowl, put the spinach, grilled Grenoble walnuts, feta cheese, grapes and apples. Add the dressing and make sure all the ingredients are mixed.
4. The salad is ready to serve. Garnish each plate with a lemon wedge.
If you are allergic to tree nuts, you can use pumpkin seeds instead of Grenoble walnuts.