In a 9x13 inch sheet pan, toss the beets with the olive oil, Italian seasoning, and salt.
Place the pan in the preheated oven and roast for 20 to 25 minutes, or until beets are soft when pierced with a fork. Remove from the oven and set aside.
Make the dressing:
In a medium bowl, whisk together the olive oil, white balsamic vinegar, mustard, maple syrup, and salt.
Assemble the salad:
Place the spinach in a large serving bowl to form a salad bed. Top with the warm roasted beets and evenly distribute the cheese (if using) and walnuts over the top. Drizzle with the dressing and serve.