1. In a large serving bowl, whisk together pomegranate juice, vinegar, and oil.
2. Peel pumpkin. With a vegetable peeler, cut raw pumpkin into paper-thin 1- by 3-inch strips; you'll need about 2 1/2 cups. Add pumpkin shavings to pomegranate vinaigrette and mix gently.
3. Add spinach and mix to coat; add salt and pepper to taste. Sprinkle with pumpkin seeds.