To toast the pistachio nuts, preheat the oven to 350 degrees Fahrenheit. Arrange the pistachio nuts in a single layer in a small pan and roast until you can just detect their aroma and they are lightly browned, about 5 minutes. Let them cool to room temperature, then chop them coarsely (this can be done ahead). Toast the quinoa in a medium skillet over high heat, shaking the pan occasionally, until it lightly browns, starts to crackle, and smells a bit toasted, about 5 minutes. Transfer to a pot, add the water and the salt, cover, and bring to a simmer. Cook until the quinoa is soft but still has a little bite, about 15 minutes. The water should be gone. Transfer the grain to a bowl and let it cool. Add the pistachio nuts, celery, scallions, and cranberries and toss everything together. If not serving immediately, refrigerate the salad, but bring it to room temperature before serving.