1. Preheat oven to 375°F. Wrap beets individually in foil, and place on baking sheet. Roast 1 hour, or until tender. Cool.
2. Meanwhile, pour orange juice over goji berries in small bowl. Soak goji berries 1 hour, or until plump and softened.
3. When beets are cool enough to handle, rub off skins using paper towel, then cut beets into thin slices.
4. Strain goji berries into small, clean bowl, and reserve juice. Whisk together 2 Tbs. reserved juice with mustard, vinegar, and oil in separate bowl.
5. Toss spinach with dressing in large bowl, and season with salt and pepper, if desired. Sprinkle with goji berries, beets, cranberries, and pumpkin seeds.