Pre-heat the oven at 375 degrees. Line a baking dish with non-stick foil. In a large bowl, toss the potatoes and mushrooms with olive oil and spices. Bake on the middle rack and stir the ingredients after 20 minutes. Bake for another 15 minutes (or until the potatoes are tender). Add the spinach and mix well. Bake for another 5 minutes. Serve immediately.