Rip spinach and place in a vegetable steamer on the stove, with a small amount of water. Steam lightly for about 30 seconds, until spinach is warm but not completely wilted.

With a sharp knife, cut, peel and white pith membrane from orange. Using a small sharp knife, cut between inner membranes to release segments. Transfer to a large bowl. Add the spinach.

Blend the walnut oil, vinegar, salt and pepper, and spoon mixture over the orange and spinach in the bowl. Toast walnuts and sprinkle over salad. Add salt and pepper to taste, and sprinkle with cheese. Serve immediately.