Flatten pork slices to 1/2-in. thickness. In a shallow dish, combine the ground walnuts, flour, 1/4 teaspoon salt and 1/4 teaspoon pepper. Add pork, a few pieces at a time, and turn to coat.
In a large skillet over medium heat, cook pork in oil in batches on each side or until meat is no longer pink, 2-3 minutes. Remove and keep warm.
In the same skillet, saute shallot until tender. Add pear; cook 1 minute longer. Add the broth, preserves and vinegar. Bring to a boil; cook until slightly thickened, 6-8 minutes. Stir in the rosemary, sage and remaining 1/4 teaspoon salt and 1/4 teaspoon pepper. Remove from the heat.
Place spinach in a large bowl. Add pear mixture; toss to coat. Divide among 6 plates; top each with pork. Sprinkle with cheese and chopped walnuts.