In a food processor bowl, combine the spinach, pine nuts, lemon zest and lemon juice. With the machine running, gradually add the oil, blending until the mixture is creamy. Transfer the pesto to a medium bowl. Stir in the Parmesan cheese and 1/2 teaspoon each of salt and pepper. Season the pesto with more salt and pepper to taste. The pesto can be made 2 days ahead. Cover and refrigerate.