Toast walnuts in a nonstick skillet over medium heat, stirring frequently to prevent scorching, about 5 minutes or until fragrant. Transfer walnuts to a plate, and set aside.
Use a microplane grater or vegetable peeler ok to remove the zest from the orange (only the colorful skin, not the bitter white part underneath). If using a vegetable peeler, chop the zest finely; place zest in a large bowl. Carefully peel the orange with a knife, removing all of the white pith and outer membrane. Hold the fruit over the bowl and cut between the inner membranes to release the orange segments; let them drop into the bowl, along with the juices. Use clean hands to tear larger segments into smaller pieces.
Add olive oil and salt; toss until combined. Add barley, fennel, sun-dried tomatoes, and reserved walnuts. Toss until thoroughly combined.