Prepare Citrus Vinaigrette; reserve. Cut beef steak into 1/8- inch thick strips; cut each strip in half. Heat oil in a large nonstick skillet over medium-high heat. Stir-fry beef(1/2 at a time) 1 to 2 minutes. Remove with slotted spoon; season with salt, if desired. Toss lettuce, beef and oranges in large bowl. Sprinkle with walnuts. Drizzle with Citrus Vinaigrette. Garnish with strawberries, if desired. Serve immediately.

Recipe may also be prepared using beef top round steak cut 1 inch thick or flank steak.