Cook orzo in boiling water according to package directions, omitting salt and fat. Drain pasta in a colander over a bowl, reserving 1/4 cup cooking liquid. Heat a large skillet over medium-high heat. Add olive oil to pan; swirl to coat. Add orzo, salt, and black pepper; cook 1 minute, stirring constantly. Stir in reserved 1/4 cup cooking liquid, white balsamic vinegar, and spinach; cook for 2 minutes or until spinach wilts.