Heat the oil in a large pot or Dutch oven over medium heat. Add the garlic and cook, turning occasionally, until lightly golden, 3 to 4 minutes. Add the raisins, pistachios, and vinegar to the pot and stir to plump the raisins, about 1 minute.
Add as much spinach to the pot as will fit and cook, tossing and adding more spinach as there is room, until just wilted, 2 to 3 minutes. Season with ½ teaspoon salt and ¼ teaspoon pepper. Serve immediately.