Toast walnuts: add walnuts into a skillet over medium heat and toast for 2-5 minutes or until fragrant, tossing occasionally. Remove from pan and let cool.
Make salad: In a large bowl combine diced apple, grapes, celery, walnuts, yogurt, lemon juice as well as raisins and parsley (if using). Taste and season with salt and add pepper if desired.
Serve: Serve salad over a bed of lettuce, if desired.
Storage: Salad will keep in the fridge in an airtight container for 3-4 days.
Notes
Vegan option: use a dairy-free yogurt like Culina coconut yogurt or a vegan mayonnaise.
Yogurt sub: You can use mayonnaise in place of yogurt or even do 1/4 cup yogurt and 1/4 cup mayo.
For a sweeter version: add 1 teaspoon maple syrup or honey.