The beautiful balance of sweet, sour, and salty tastes comes through in this simple salad. You might want to make a double batch and enjoy leftovers the next day, since hearty spinach stands up to the light lemon vinaigrette.
Fill a medium saucepan halfway with water and bring to a boil on high heat. Stir in the orzo, add 1 pinch of salt, and boil for 8 to 10 minutes until al dente. Drain in a fine colander and pour onto a large plate. Drizzle on 1 tablespoon of oil, separating orzo into sections with a spoon to speed cooling to room temperature.
Toss together in a medium bowl the cooled orzo, remaining tablespoon of oil, spinach, grapes, celery, pistachios, scallions, Parmesan cheese, lemon juice, salt, and pepper.
Eat immediately or chill until ready to serve, up to 2 days.