Into medium bowl, pour 3 cups boiling water over porcini; let stand 10 minutes.
Meanwhile, cut steak lengthwise in half. With knife held in a slanted position, almost parallel to cutting surface, slice each half of steak crosswise into 1/8-inch-thick slices.

In deep nonstick 12-inch skillet, heat oil over medium-high heat until very hot. Add half of steak slices and cook 2 minutes or until steak just loses its pink color, stirring constantly. Transfer steak to medium bowl; repeat with remaining steak. Toss steak with soy sauce; set aside.

To same skillet, add white mushrooms, carrots, onion, salt, pepper, and thyme and cook 10 minutes over medium-high heat or until vegetables are tender-crisp, stirring occasionally.

While vegetables are cooking, with slotted spoon, remove porcini from soaking liquid, reserving liquid. Rinse porcini to remove any sand; coarsely chop. Strain soaking liquid through sieve lined with paper towel into medium bowl.
Add barley, broth, porcini, and soaking liquid to vegetables in skillet; heat mixture to boiling over medium-high heat. Reduce heat to medium-low; cover and simmer 35 to 40 minutes or until barley and vegetables are tender and most of liquid has evaporated, stirring occasionally. Stir in steak mixture and parsley; heat through.